Create 15. 3Sum

Author: stone16

15. 3Sum

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+public class Solution {
+    public List<List<Integer>> threeSum(int[] nums) {
+        List<List<Integer>> results = new ArrayList<>();
+        if( nums == null || nums.length <= 2){
+            return results;
+        }
+        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){
+                if(nums[i] + nums[left] + nums[right] > 0){
+                    right --;
+                    
+                    }else if(nums[i] + nums[left] + nums[right] == 0){
+                    ArrayList <Integer> list = new ArrayList<>();
+                    list.add(nums[i]);
+                    list.add(nums[left]);
+                    list.add(nums[right]);
+                    results.add(list);
+                    left ++;
+                    right --;
+                    while(left < right && nums[left] == nums[left - 1]){// 关键点！！！
+                        left ++;
+                    }
+                    while(right > left  && nums[right] == nums[right + 1]){
+                        right --;
+                    }
+                }else{
+                    left ++;
+                   
+                }
+            }
+        }
+        return results;
+    }
+}