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Merge pull request #1524 from Tessa1217/main
[Tessa1217] Week 09 Solutions
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โ€Žlinked-list-cycle/Tessa1217.javaโ€Ž

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/**
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* Definition for singly-linked list.
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* class ListNode {
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* int val;
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* ListNode next;
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* ListNode(int x) {
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* val = x;
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* next = null;
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* }
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* }
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*/
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/**
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* head๋Š” ์—ฐ๊ฒฐ ๋ฆฌ์ŠคํŠธ์˜ ํ—ค๋“œ๋‹ค.
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* ํŠน์ • ๋…ธ๋“œ๊ฐ€ ๋ฆฌ์ŠคํŠธ ๋‚ด์˜ ๋‹ค๋ฅธ ๋…ธ๋“œ์™€ next ํฌ์ธํŠธ๋ฅผ ํ†ตํ•ด ์—ฐ๊ฒฐ๋˜์–ด ์žˆ์„ ๋•Œ ์ด ๋ฆฌ์ŠคํŠธ์—๋Š” ์‚ฌ์ดํด์ด ์žˆ๋‹ค๊ณ  ํ•  ์ˆ˜ ์žˆ๋‹ค.
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* pos๋Š” next ํฌ์ธํ„ฐ์™€ ์—ฐ๊ฒฐ๋œ ๋…ธ๋“œ์˜ ์ธ๋ฑ์Šค๋ฅผ ๋‚˜ํƒ€๋‚ด๋Š”๋ฐ ์“ฐ์ด๋ฉฐ pos๋Š” ํŒŒ๋ผ๋ฏธํ„ฐ๋กœ ์ฃผ์–ด์ง€์ง€ ์•Š๋Š”๋‹ค.
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* ์ฃผ์–ด์ง„ ๋ฆฌ์ŠคํŠธ์— ์‚ฌ์ดํด์ด ์žˆ๋‹ค๋ฉด true๋ฅผ ๊ทธ๋ ‡์ง€ ์•Š๋‹ค๋ฉด false๋ฅผ ๋ฐ˜ํ™˜ํ•˜์„ธ์š”.
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* */
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public class Solution {
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// ์‹œ๊ฐ„๋ณต์žก๋„: O(n), ๊ณต๊ฐ„๋ณต์žก๋„: O(1)
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public boolean hasCycle(ListNode head) {
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if (head == null) {
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return false;
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}
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ListNode next = head;
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ListNode furtherNext = head;
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while (furtherNext != null && furtherNext.next != null) {
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next = next.next;
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furtherNext = furtherNext.next.next;
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if (next == furtherNext) {
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return true;
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}
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}
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return false;
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}
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// head ์—†์„ ๋•Œ๊นŒ์ง€ ๊ณ„์† ํƒ์ƒ‰ ๋ฐ˜๋ณต : ์‹œ๊ฐ„๋ณต์žก๋„, ๊ณต๊ฐ„๋ณต์žก๋„ O(n)
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// public boolean hasCycle(ListNode head) {
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// Set<ListNode> nodeSet = new HashSet<>();
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// while (head != null) {
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// if (nodeSet.contains(head)) {
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// return true;
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// }
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// nodeSet.add(head);
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// head = head.next;
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// }
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// return false;
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// }
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}
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โ€Žmaximum-product-subarray/Tessa1217.javaโ€Ž

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class Solution {
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// ์‹œ๊ฐ„๋ณต์žก๋„: O(n)
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public int maxProduct(int[] nums) {
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if (nums == null || nums.length == 0) {
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return 0;
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}
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// ์ตœ๋Œ€ ๊ณฑ ์ผ€์ด์Šค
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int maxProduct = nums[0];
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// ์ตœ์†Œ ๊ณฑ ์ผ€์ด์Šค
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int minProduct = nums[0];
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// ์ตœ๋Œ€ ๊ฐ’
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int max = nums[0];
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// DP๋กœ ํ’€์ดํ•˜์˜€์ง€๋งŒ ์Œ์ˆ˜ * ์Œ์ˆ˜์˜ ๋ฐ˜๋ก€ ์ผ€์ด์Šค ๋ฐœ์ƒํ•˜์—ฌ ํ•ด๋‹น ํ’€์ด๋กœ ์ˆ˜์ •
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// Test Case : [-2, 3, -4] => dp๋กœ ํ’€์ด ์‹œ 3์ด ๋ฐ˜ํ™˜๋˜๋Š” ๋ฌธ์ œ ์žˆ์—ˆ์Œ
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for (int i = 1; i < nums.length; i++) {
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int current = nums[i];
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// ์Œ์ˆ˜์ผ ๊ฒฝ์šฐ : ์ตœ์†Œ ๊ณฑ๊ณผ ์ตœ๋Œ€ ๊ณฑ ์œ„์น˜ ๋ฐ”๊ฟˆ
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if (current < 0) {
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int tempMax = maxProduct;
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maxProduct = Math.max(current, minProduct * current);
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minProduct = Math.min(current, tempMax * current);
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} else {
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maxProduct = Math.max(current, maxProduct * current);
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minProduct = Math.min(current, minProduct * current);
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}
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max = Math.max(max, maxProduct);
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}
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return max;
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}
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}
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โ€Žminimum-window-substring/Tessa1217.javaโ€Ž

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import java.util.HashMap;
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import java.util.Map;
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class Solution {
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// ์‹œ๊ฐ„๋ณต์žก๋„: O(n), ๊ณต๊ฐ„๋ณต์žก๋„ O(1)
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public String minWindow(String s, String t) {
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int strLength = s.length();
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int targetLength = t.length();
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// ๋ชฉํ‘œ ๋ถ„์ž์—ด์ด ์ฃผ์–ด์ง„ ๋ฌธ์ž์—ด๋ณด๋‹ค ๊ธธ๋‹ค๋ฉด ๋ถ€๋ถ„ ๋ฌธ์ž์—ด๋กœ ๋ณผ ์ˆ˜ ์—†์Œ
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if (targetLength > strLength) {
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return "";
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}
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// ๋ชฉํ‘œ ๋ฌธ์ž์—ด์— ํ•„์š”ํ•œ ๋ฌธ์ž์™€ ๊ทธ ๊ฐœ์ˆ˜๋ฅผ ๋‹ด๋Š” ๋งต
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Map<Character, Integer> charMap = new HashMap<>();
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for (char c : t.toCharArray()) {
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charMap.put(c, charMap.getOrDefault(c, 0) + 1);
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}
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// ํˆฌ ํฌ์ธํ„ฐ ์„ ์–ธ
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int left = 0;
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int right = 0;
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int minWindowLength = Integer.MAX_VALUE;
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int minWindowStart = 0; // ์ตœ์†Œ ์œˆ๋„์šฐ ์‹œ์ž‘ ์œ„์น˜
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int remaining = targetLength;
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while (right < strLength) {
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Character end = s.charAt(right);
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if (charMap.containsKey(end)) {
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charMap.put(end, charMap.get(end) - 1);
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if (charMap.get(end) >= 0) {
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remaining--;
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}
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}
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// target ๋ฌธ์ž์—ด์˜ ๋ชจ๋“  ๋ฌธ์ž๋ฅผ ์ฐพ์•˜๋‹ค๋ฉด left ํฌ์ธํ„ฐ ์ด๋™ํ•˜๋ฉด์„œ
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// ์ตœ์†Œ ์œˆ๋„์šฐ ์ฐพ๊ธฐ ์‹œ์ž‘
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while (remaining == 0) {
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if (right - left + 1 < minWindowLength) {
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minWindowLength = right - left + 1;
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minWindowStart = left;
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}
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char startChar = s.charAt(left);
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if (charMap.containsKey(startChar)) {
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charMap.put(startChar, charMap.get(startChar) + 1);
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if (charMap.get(startChar) > 0) {
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remaining++;
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}
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}
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left++;
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}
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right++;
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}
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return minWindowLength == Integer.MAX_VALUE ? ""
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: s.substring(minWindowStart, minWindowStart + minWindowLength);
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}
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}
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โ€Žpacific-atlantic-water-flow/Tessa1217.javaโ€Ž

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import java.util.ArrayList;
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import java.util.List;
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class Solution {
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int[] dx = {1, -1, 0, 0};
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int[] dy = {0, 0, 1, -1};
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// boolean[][] visited;
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int width, height;
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// ์‹œ๊ฐ„๋ณต์žก๋„, ๊ณต๊ฐ„๋ณต์žก๋„: O(m * n)
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public List<List<Integer>> pacificAtlantic(int[][] heights) {
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height = heights.length;
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width = heights[0].length;
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boolean[][] pacific = new boolean[height][width];
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boolean[][] atlantic = new boolean[height][width];
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/**
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* ๊ฐ€์žฅ์ž๋ฆฌ์— ๋„๋‹ฌํ•˜๋Š” ๊ฒฝ๋กœ๋ฅผ ์ผ์ผ์ด ํƒ์ƒ‰ํ•˜๋Š” ๊ฒƒ์ด ์•„๋‹Œ
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๊ฐ€์žฅ์ž๋ฆฌ๋ถ€ํ„ฐ ๋ฌผ์ด ํ๋ฅผ ์ˆ˜ ์žˆ๋Š” ๊ฒฝ๋กœ๋ฅผ ์—ญ์œผ๋กœ ํƒ์ƒ‰
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*/
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// height check
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for (int i = 0; i < height; i++) {
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dfs(i, 0, heights, pacific);
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dfs(i, width - 1, heights, atlantic);
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}
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// width check
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for (int j = 0; j < width; j++) {
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dfs(0, j, heights, pacific);
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dfs(height - 1, j, heights, atlantic);
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}
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List<List<Integer>> answer = new ArrayList<>();
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for (int i = 0; i < height; i++) {
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for (int j = 0; j < width; j++) {
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if (pacific[i][j] && atlantic[i][j]) {
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answer.add(List.of(i, j));
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}
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}
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}
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return answer;
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}
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private void dfs(int x, int y, int[][] heights, boolean[][] visited) {
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visited[x][y] = true;
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for (int i = 0; i < 4; i++) {
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int nx = x + dx[i];
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int ny = y + dy[i];
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if (nx >= 0 && nx < height && ny >= 0 && ny < width) {
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if (!visited[nx][ny] && heights[nx][ny] >= heights[x][y]) {
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dfs(nx, ny, heights, visited);
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}
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}
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}
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}
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// public List<List<Integer>> pacificAtlantic(int[][] heights) {
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// height = heights.length;
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// width = heights[0].length;
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// visited = new boolean[height][width];
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// List<List<Integer>> answer = new ArrayList<>();
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// for (int i = 0; i < height; i++) {
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// for (int j = 0; j < width; j++) {
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// WaterFlow checkWaterFlow = dfs(i, j, new WaterFlow(), heights);
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// if (checkWaterFlow.crossBothOceans()) {
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// List<Integer> coordinate = List.of(i, j);
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// answer.add(coordinate);
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// }
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// }
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// }
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// return answer;
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// }
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// private WaterFlow dfs(int x, int y, WaterFlow checkWaterFlow, int[][] heights) {
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// /**
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// 0, 0 | 0, 1 | 0, 2 | 0, 3 | 0, 4
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// 1, 0 | 2, 0 | 3, 0 | 4, 0
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// */
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// if (x == 0 || y == 0) {
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// checkWaterFlow.crossPacificFlow();
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// }
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// /**
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// 4, 0 | 4, 1 | 4, 2 | 4, 3 | 4, 4
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// 3, 4 | 2, 4 | 1, 4 | 0, 4
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// */
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// if (x == height - 1 || y == width - 1) {
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// checkWaterFlow.crossAtlanticFlow();
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// }
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// if (checkWaterFlow.crossBothOceans()) {
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// return checkWaterFlow;
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// }
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// visited[x][y] = true;
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// for (int i = 0; i < 4; i++) {
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// int nx = x + dx[i];
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// int ny = y + dy[i];
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// if (nx >= 0 && nx < height && ny >= 0 && ny < width) {
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// if (!visited[nx][ny] && heights[nx][ny] <= heights[x][y]) {
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// dfs(nx, ny, checkWaterFlow, heights);
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// }
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// }
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// }
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// visited[x][y] = false;
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// return checkWaterFlow;
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// }
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// static class WaterFlow {
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// private boolean pacificFlow;
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// private boolean atlanticFlow;
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// WaterFlow() {
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// pacificFlow = false;
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// atlanticFlow = false;
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// }
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// public void crossPacificFlow() {
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// pacificFlow = true;
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// }
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// public void crossAtlanticFlow() {
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// atlanticFlow = true;
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// }
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// public boolean crossBothOceans() {
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// return pacificFlow && atlanticFlow;
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// }
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// }
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}
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โ€Žsum-of-two-integers/Tessa1217.javaโ€Ž

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/** +, - ๋ถ€ํ˜ธ ์“ฐ์ง€ ์•Š๊ณ  ๋‘ ์ˆ˜์˜ ํ•ฉ ๊ตฌํ•˜๊ธฐ */
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class Solution {
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// ๋น„ํŠธ ์—ฐ์‚ฐ์œผ๋กœ ๊ณ„์‚ฐ ์ˆ˜ํ–‰
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public int getSum(int a, int b) {
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while (b != 0) {
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// ์™ผ์ชฝ ์‰ฌํ”„ํŠธํ•˜์—ฌ ์ž๋ฆฌ ์˜ฌ๋ฆผ์— ๋Œ€ํ•œ ๊ณ„์‚ฐ ์ˆ˜ํ–‰
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int bit = (a & b) << 1;
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// XOR ์—ฐ์‚ฐ์œผ๋กœ ์ž๋ฆฌ ์˜ฌ๋ฆผ ์—†๋Š” ๋ง์…ˆ ์ˆ˜ํ–‰
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a = a ^ b;
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b = bit;
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}
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return a;
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}
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/**
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* ํ’€๋ฆฌ๊ธฐ๋Š” ํ•˜์ง€๋งŒ, ์ด๋Ÿฐ ์‹์€ ํŽธ๋ฒ•์ผ ๊ฒƒ ๊ฐ™์€...?
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* Class Integer ๋‚ด๋ถ€์— sum ์—ฐ์‚ฐ: Adds two integers together as per the + operator.
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* + operator ์“ด๋‹ค๊ณ  ๋˜์–ด์žˆ์Œ...
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* */
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// public int getSum(int a, int b) {
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// return Integer.sum(a, b);
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// }
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}
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