Merge pull request #710 from dalpang81/main

[wonYeong] Week2

Author: lwy-0418

3sum/dalpang81.java

@@ -0,0 +1,47 @@
+/*
+* 시간복잡도 : O(N^2)
+* 공간복잡도 : O(1)
+* */
+import java.util.*;
+
+class Solution {
+    public List<List<Integer>> threeSum(int[] nums) {
+        List<List<Integer>> result = new ArrayList<>();
+        Arrays.sort(nums);
+
+        for (int i = 0; i < nums.length - 2; i++) {
+            if (i > 0 && nums[i] == nums[i - 1]) {
+                continue;
+            }
+
+            int left = i + 1;
+            int right = nums.length - 1;
+
+            while (left < right) {
+                int sum = nums[i] + nums[left] + nums[right];
+
+                if (sum == 0)
+                {
+                    // 합이 0인 경우 결과에 추가
+                    result.add(Arrays.asList(nums[i], nums[left], nums[right]));
+
+                    // 중복된 값 건너뛰기
+                    while (left < right && nums[left] == nums[left + 1])
+                        left++;
+
+                    while (left < right && nums[right] == nums[right - 1])
+                        right--;
+
+                    left++;
+                    right--;
+                }
+                else if (sum < 0)
+                    left++;
+                 else
+                    right--;
+
+            }
+        }
+        return result;
+    }
+}

climbing-stairs/dalpang81.java

@@ -0,0 +1,19 @@
+/*
+시간복잡도 : O(n)
+ 공간복잡도 : O(n)
+ */
+class Solution {
+    public int climbStairs(int n) {
+        if (n <= 2) return n;
+
+        int[] dp = new int[n + 1];
+        dp[1] = 1;
+        dp[2] = 2;
+
+        for(int i = 3; i <= n; i++)
+            dp[i] = dp[i - 1] + dp[i - 2];
+
+        return dp[n];
+
+    }
+}

valid-anagram/dalpang81.java

@@ -0,0 +1,26 @@
+/*
+ 시간복잡도 : O(N)
+ 공간복잡도 : O(1)
+ */
+
+class Solution {
+    public boolean isAnagram(String s, String t) {
+        if(s.length() != t.length()) return false;
+
+        int[] character = new int[26];
+
+        for(int i = 0; i < s.length(); i++) {
+            character[s.charAt(i) - 'a']++;
+            character[t.charAt(i) - 'a']--;
+        }
+
+
+        for(int num : character) {
+            if(num != 0)
+                return false;
+        }
+
+        return true;
+
+    }
+}