Merge pull request #1731 from renovizee/main

[renovziee] WEEK 02 Solutions

Author: renovizee

3sum/renovizee.java

@@ -0,0 +1,19 @@
+import java.util.List;
+
+
+// tag renovizee 2week unresolved
+// https://github.com/DaleStudy/leetcode-study/issues/241
+// https://leetcode.com/problems/3sum/
+class Solution {
+    // Solv1 :
+    // 시간복잡도 : O(n)
+    // 공간복잡도 : O(n)
+    public List<List<Integer>> threeSum(int[] nums) {
+
+    }
+}
+
+//-------------------------------------------------------------------------------------------------------------
+// Java 문법 피드백
+//
+//-------------------------------------------------------------------------------------------------------------

climbing-stairs/renovizee.java

@@ -0,0 +1,35 @@
+
+
+
+// tag renovizee 2week
+// https://github.com/DaleStudy/leetcode-study/issues/230
+// https://leetcode.com/problems/climbing-stairs/ #70 #Easy
+class Solution {
+    // Solv1
+    // 시간복잡도 : O(n)
+    // 공간복잡도 : O(n)
+    public int climbStairs(int n) {
+        int[] dp = new int[]{1, 2};
+
+        if (n == dp[0]) {
+            return dp[0];
+        }
+
+        if (n == dp[1]) {
+            return dp[1];
+        }
+
+        for (int i = 3; i <= n; i++) {
+            int nextWayCount = dp[0] + dp[1];
+            dp[0] = dp[1];
+            dp[1] = nextWayCount;
+        }
+
+        return dp[1];
+
+    }
+}
+//-------------------------------------------------------------------------------------------------------------
+// Java 문법 피드백
+// 1) Math.pow(2, 3) 2의 3승.
+//-------------------------------------------------------------------------------------------------------------

house-robber/renovizee.java

@@ -1,6 +1,8 @@
 
+// tag renovizee 1week unresolved
 // https://github.com/DaleStudy/leetcode-study/issues/264
 // https://leetcode.com/problems/house-robber/
+// DP 자체에 대한 설명 : https://www.youtube.com/watch?v=0bqfTzpWySY
 class Solution {
     public int rob(int[] nums) {
 

product-of-array-except-self/renovizee.java

@@ -0,0 +1,49 @@
+
+
+// tag renovizee 2week
+// https://github.com/DaleStudy/leetcode-study/issues/239
+// https://leetcode.com/problems/product-of-array-except-self/  #238 #Medium
+class Solution {
+    // Solv1 :
+    // 시간복잡도 : O(n)
+    // 공간복잡도 : O(n)
+    public int[] productExceptSelf(int[] nums) {
+
+        boolean isZero = false;
+        int zeroIndex = 0;
+
+        int productExceptZero = 1;
+        for (int i = 0; i < nums.length; i++) {
+            if (nums[i] == 0) {
+                if (isZero) { // zero가 2개면 모든 원소가 0임.
+                    return new int[nums.length];
+                }
+                zeroIndex = i;
+                isZero = true;
+            } else {
+                productExceptZero *= nums[i];
+            }
+        }
+
+        int[] result = new int[nums.length];
+        for (int i = 0; i < nums.length; i++) {
+            if (isZero) {
+                if (i != zeroIndex) {
+                    result[i] = 0;
+                } else {
+                    result[i] = productExceptZero;
+                }
+            } else {
+                result[i] = productExceptZero / nums[i];
+            }
+
+        }
+        return result;
+    }
+
+}
+
+//-------------------------------------------------------------------------------------------------------------
+// Java 문법 피드백
+//
+//-------------------------------------------------------------------------------------------------------------

top-k-frequent-elements/renovizee.java

@@ -1,7 +1,9 @@
 
+// tag renovizee 1week unresolved
 // https://github.com/DaleStudy/leetcode-study/issues/237
 // https://leetcode.com/problems/top-k-frequent-elements/
 class Solution {
+
     public int[] topKFrequent(int[] nums, int k) {
         int[] result = {1, 2, 3};
 

valid-anagram/renovizee.java

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+import java.util.Arrays;
+
+// tag renovizee 2week
+// https://github.com/DaleStudy/leetcode-study/issues/218
+// https://leetcode.com/problems/valid-anagram/ #242 #Easy
+class Solution {
+    // Solv1
+    // 시간복잡도 : O(n)
+    // 공간복잡도 : O(n)
+    public boolean isAnagram(String s, String t) {
+
+        char[] sChars = s.toCharArray();
+        char[] tChars = t.toCharArray();
+
+        Arrays.sort(sChars);
+        Arrays.sort(tChars);
+
+        return Arrays.equals(sChars, tChars);
+    }
+}
+
+//-------------------------------------------------------------------------------------------------------------
+// Java 문법 피드백
+// 1) string.toCharArray
+// 2) Arrays.~ 문법 ~.sort ~.equals
+// 3) Arrays.
+//-------------------------------------------------------------------------------------------------------------

validate-binary-search-tree/renovizee.java

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+
+
+// tag renovizee 2week
+// https://github.com/DaleStudy/leetcode-study/issues/251
+// https://leetcode.com/problems/validate-binary-search-tree/
+class Solution {
+
+    /**
+     * Definition for a binary tree node.
+     * public class TreeNode {
+     *     int val;
+     *     TreeNode left;
+     *     TreeNode right;
+     *     TreeNode() {}
+     *     TreeNode(int val) { this.val = val; }
+     *     TreeNode(int val, TreeNode left, TreeNode right) {
+     *         this.val = val;
+     *         this.left = left;
+     *         this.right = right;
+     *     }
+     * }
+     */
+
+    // Solv1 :
+    // 시간복잡도 : O(n)
+    // 공간복잡도 : O(n)
+    public boolean isValidBST(TreeNode root) {
+
+    }
+}
+
+//-------------------------------------------------------------------------------------------------------------
+// Java 문법 피드백
+//
+//-------------------------------------------------------------------------------------------------------------