leetcode_four_sum

发表于

难度:Medium
解题思路：可以按照3Sum的思路来。代码如下。

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class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int>> ret;
        if(nums.size()<4) return ret;
        sort(nums.begin(),nums.end());
        for(int i = 0; i < nums.size()-3; i++)
        {
            if(i!=0 && nums[i]==nums[i-1]) continue;
            for(int j = i+1; j < nums.size()-2; j++)
            {
                if(j!=i+1 && nums[j]==nums[j-1]) continue;
                int low = j+1;
                int high = nums.size()-1;
                while(low < high)
                {
                    if(low != j+1 && nums[low]==nums[low-1])
                    {
                        low++;
                        continue;
                    }
                    if(high != nums.size()-1 && nums[high]==nums[high+1]){
                        high--;
                        continue;
                    }
                    int sum = nums[i]+nums[j]+nums[low]+nums[high];
                    if(sum == target)
                    {
                        ret.push_back({nums[i],nums[j],nums[low],nums[high]});
                        high--;
                    }
                    else if(sum > target)
                        high--;
                    else 
                        low++;
                }
            }
        }
        return ret;
    }
};