18. 4Sum

标签：ica   code   integer   note   tar   continue   level   eve   ||   

Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note:

The solution set must not contain duplicate quadruplets.

Example:

Given array nums = [1, 0, -1, 0, -2, 2], and target = 0.

A solution set is:
[
  [-1,  0, 0, 1],
  [-2, -1, 1, 2],
  [-2,  0, 0, 2]
]

class Solution {
    public List<List<Integer>> fourSum(int[] nums, int target) {
        List<List<Integer>> res = new ArrayList<>();
        if(nums == null || nums.length <= 0) return res;
        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, right = nums.length - 1;
                int tmpTarget = target - nums[i] - nums[j];
                while(left < right) {
                    if(nums[left] + nums[right] < tmpTarget) {
                        left++;
                    }
                    else if(nums[left] + nums[right] > tmpTarget) {
                        right--;
                    }
                    else {
                        List<Integer> level = new ArrayList<>();
                        level.add(nums[i]);
                        level.add(nums[j]);
                        level.add(nums[left]);
                        level.add(nums[right]);
                        res.add(level);
                        left++;
                        right--;
                        while(left < right && nums[left] == nums[left-1]) {
                            left++;
                        }
                        while(left < right && nums[right] == nums[right+1]){
                            right--;
                        }
                    }
                }
            }
        }
        return res;
    }
}

18. 4Sum

标签：ica   code   integer   note   tar   continue   level   eve   ||   

原文地址：https://www.cnblogs.com/lawrenceSeattle/p/10262395.html