题解 | #未排序数组中累加和为给定值的最长子数组长度#

#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;

int main() {
    int n; 
    int target;
    std::vector<int> nums;
    int num;
    std::unordered_map<int, int> umap; // <sum, pos> 值为sum最早出现的pos
    int sum;
    int max_len;
    while (std::cin >> n) {
        std::cin >> target;
        nums.resize(n);
        for (int i = 0; i < n; i++) {
            std::cin >> num;
            nums[i] = num;
        }

        umap.clear();
        umap[0] = -1; // 提前填充的 note 
        sum = 0;
        max_len = 0;
        for (int i = 0; i < n; i++) {
            sum += nums[i];
            auto itr = umap.find(sum - target);
            if (itr != umap.end()) {
                max_len = std::max(max_len, i - itr->second);
            }
            if (umap.find(sum) == umap.end()) {
                umap[sum] = i; // 第一次出现sum的值加入
            }
        }
        std::cout << max_len << std::endl;

    }
}
// 64 位输出请用 printf("%lld")