LeetCode 454.四数相加
题目链接: LeetCode454
思路: 将两个数组中的数存放到一个map中，用另外两个数组的值在map中去减
class Solution {
public:
int fourSumCount(vector<int>& A, vector<int>& B, vector<int>& C, vector<int>& D) {
unordered_map<int, int> umap;
for (int a : A) {
for (int b : B) {
umap[a + b]++;
}
}
int count = 0;
for (int c : C) {
for (int d : D) {
if (umap.find(0 - (c + d)) != umap.end()) {
count += umap[0 - (c + d)];
}
}
}
return count;
}
};
LeetCode 15.三数之和
题目链接: LeetCode15
思路:
LeetCode 18.四数之和
题目链接: LeetCode18
思路:
标签：四数,15,int,454,随想录,umap,vector,三数 From： https://www.cnblogs.com/ygmzj/p/17877848.html