3sum solution

Author: hyunolike

3sum/hyunolike.java

@@ -0,0 +1,41 @@
+class Solution {
+    public List<List<Integer>> threeSum(int[] nums) {
+        List<List<Integer>> result = new ArrayList<>();
+
+        int n = nums.length;
+        if (n < 3) return result;
+
+        Arrays.sort(nums);
+
+        for(int i = 0; i < n - 2; i++) {
+            if(i > 0 && nums[i] == nums[i-1]) continue;
+
+            int left = i + 1;
+            int right = n - 1;
+
+            while(left < right) {
+                int sum = nums[i] + nums[left] + nums[right];
+
+                if(sum < 0){
+                    left++;
+                }
+                else if(sum > 0) {
+                    right --;
+                }
+                else {
+                                       // sum == 0 → 조합 하나 찾음
+                    result.add(Arrays.asList(nums[i], nums[left], nums[right]));
+
+                    // left, right 중복값 스킵
+                    int leftVal = nums[left];
+                    int rightVal = nums[right];
+
+                    while (left < right && nums[left] == leftVal) left++;
+                    while (left < right && nums[right] == rightVal) right--;
+                }
+            }
+        }
+
+        return result;
+    }
+}