Create 18. 4Sum

Author: stone16

18. 4Sum

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+public class Solution {
+    public List<List<Integer>> fourSum(int[] nums, int target) {
+ List<List<Integer>> rst = new ArrayList<List<Integer>>();
+		Arrays.sort(nums);
+
+		for (int i = 0; i < nums.length - 3; i++) {
+			if (i != 0 && nums[i] == nums[i - 1]) {
+				continue;
+			}
+
+			for (int j = i + 1; j < nums.length - 2; j++) {
+				if (j != i + 1 && nums[j] == nums[j - 1])
+					continue;
+
+				int left = j + 1;
+				int right = nums.length - 1;
+				while (left < right) {
+					int sum = nums[i] + nums[j] + nums[left] + nums[right];
+					if (sum < target) {
+						left++;
+					} else if (sum > target) {
+						right--;
+					} else {
+						ArrayList<Integer> tmp = new ArrayList<Integer>();
+						tmp.add(nums[i]);
+						tmp.add(nums[j]);
+						tmp.add(nums[left]);
+						tmp.add(nums[right]);
+						rst.add(tmp);
+						left++;
+						right--;
+						while (left < right && nums[left] == nums[left - 1]) {
+							left++;
+						}
+						while (left < right && nums[right] == nums[right + 1]) {
+							right--;
+						}
+					}
+				}
+			}
+		}
+
+		return rst;
+	
+    }
+}