问题描述
给你一个由 n 个整数组成的数组 nums ，和一个目标值 target 。请你找出并返回满足下述全部条件且不重复的四元组 [nums[a], nums[b], nums[c], nums[d]] （若两个四元组元素一一对应，则认为两个四元组重复）：
0 <= a, b, c, d < n
a、b、c 和 d 互不相同
nums[a] + nums[b] + nums[c] + nums[d] == target
你可以按 任意顺序 返回答案 。
问题示例
输入：nums = [1,0,-1,0,-2,2], target = 0
输出：[[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
解题思路
参考代码
class Solution {public List<List<Integer>> fourSum(int[] nums, int target) {List<List<Integer>> result = new ArrayList<>();if(nums == null || nums.length < 4) {return result;}Arrays.sort(nums);for(int i = 0; i < nums.length - 3; i++) {if(i > 0 && nums[i] == nums[i-1]) {continue;}if((long) nums[i] + nums[i+1] + nums[i+2] + nums[i+3] > target) {return result;}if((long) nums[i] + nums[nums.length-3] + nums[nums.length-2] + nums[nums.length-1] < target) {continue;}for(int j = i+1; j < nums.length - 2; j++) {if(j > i+1 && nums[j] == nums[j-1]) {continue;}if((long) nums[i] + nums[j] + nums[j+1] + nums[j+2] > target) {break;}if((long) nums[i] + nums[j] + nums[nums.length-2] + nums[nums.length-1] < target) {continue;}int left = j + 1, right = nums.length - 1;while(left < right) {long sum = (long) nums[i] + nums[j] + nums[left] + nums[right];if(sum > target) {right--;} else if(sum < target) {left++;} else {result.add(Arrays.asList(nums[i], nums[j], nums[left], nums[right]));while(left < right && nums[right] == nums[right-1]) {right--;}while(left < right && nums[left] == nums[left+1]) {left++;}left++;right--;}}}}return result;}
}
