Given an array nums and a target value k, find the length of the longest sub-array whose sum is equal to k. If there is no sub-array that meets the requirements, 0 is returned.
Note:
The sum of the nums array must be within the range of 32-bit signed integers.
Example 1:
Input: nums = [1, -1, 5, -2, 3], k = 3
Output: 4
Explanation: The sum of sub-arrays [1, -1, 5, -2] is equal to 3, and the length is the longest.
Example 2:
Input: nums = [-2, -1, 2, 1], k = 1
Output: 2
Explanation: The sub-array [-1, 2] sum is equal to 1, and the length is the longest.
Source: LeetCode (LeetCode)
Link: https://leetcode-cn.com/problems/maximum-size-subarray-sum-equals-k
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public class 和为k的最长子数组的长度leetcode325 {
public static int maxSubArrayLen(int[] nums, int k) {
Map<Integer, Integer> map = new HashMap<>(); // map在这里存储sum和对应的下标值
map.put(0, -1); // 这里初始化为-1，假设0,j的和为k，那么我们得到的长度就是 j-(-1)
int sum = 0;
int len = 0;
for (int j = 0; j < nums.length; j++) {
sum += nums[j];
int preSum = sum - k;
if (map.containsKey(preSum)) {
len = Math.max(len, j - map.get(preSum));
}
if (!map.containsKey(sum)) {
map.put(sum, j);
}
}
return len;
}
public static void main(String[] args) {
// System.out.println(maxSubArrayLen(new int[]{-2,-1,2,1}, 1));
System.out.println(maxSubArrayLen(new int[]{
1, -1, 5, -2, 3}, 3));
}
}