Leetcode 325. Maximum Size Subarray Sum Equals k (Medium) (cpp)

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本文介绍了解决LeetCode 325题目的方法，该题要求找出数组中和为给定值k的最长子数组长度。通过使用哈希表记录前缀和，实现了一种有效算法。

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Leetcode 325. Maximum Size Subarray Sum Equals k (Medium) (cpp)

Tag: Hash Table

Difficulty: Medium

这是一道locked题目，给评论个“赞”呗？

/*

325. Maximum Size Subarray Sum Equals k (Medium)

Given an array nums and a target value k, find the maximum length of a subarray that sums to k. If there isn't one, return 0 instead.

Note:
The sum of the entire nums array is guaranteed to fit within the 32-bit signed integer range.

Example 1:
Given nums = [1, -1, 5, -2, 3], k = 3,
return 4. (because the subarray [1, -1, 5, -2] sums to 3 and is the longest)

Example 2:
Given nums = [-2, -1, 2, 1], k = 1,
return 2. (because the subarray [-1, 2] sums to 1 and is the longest)

*/
class Solution {
public:
    int maxSubArrayLen(vector<int>& nums, int k) {
        if (nums.empty()) {
            return 0;
        }
        int sum = 0, len = 0;
        unordered_map<int, int> mapping;
        mapping[0] = -1;
        for (int i = 0; i < nums.size(); i++) {
            sum += nums[i];
            if (mapping.find(sum - k) != mapping.end()) {
                len = max(len, i - mapping[sum - k]);
            } 
            if (mapping.find(sum) == mapping.end()){
                mapping[sum] = i;
            }
        }
        return len;
    }
};