00019【unordered_map】

力扣 454 四数相加

class Solution {
public:
    int fourSumCount(vector<int>& nums1, vector<int>& nums2, vector<int>& nums3, vector<int>& nums4) {
        unordered_map<int, int> ab;
        for(int a:nums1){
            for(int b:nums2){
                ab[a+b]++;
            }
        }
        int count = 0;
        for(int c:nums3){
            for(int d:nums4){
                if(ab.find(0-c-d) != ab.end()){
                    count += ab[0-c-d];
                }
            }
        }
        return count;
    }
};

class Solution:
    def fourSumCount(self, nums1: List[int], nums2: List[int], nums3: List[int], nums4: List[int]) -> int:
        ab = dict()
        for a in nums1:
            for b in nums2:
                if a+b in ab:
                    ab[a+b]+=1
                else:
                    ab[a+b]=1
        count = 0
        for c in nums3:
            for d in nums4:
                if 0-c-d in ab:
                    count += ab[0-c-d]
        return count