Maximum Size Subarray Sum Equals k

Given an arraynumsand a target valuek, find the maximum length of a subarray that sums tok. If there isn't one, return 0 instead.

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

Example 1:

Givennums=[1, -1, 5, -2, 3],k=3,
return4. (because the subarray[1, -1, 5, -2]sums to 3 and is the longest)

Example 2:

Givennums=[-2, -1, 2, 1],k=1,
return2. (because the subarray[-1, 2]sums to 1 and is the longest)

Follow Up:
Can you do it in O(n) time?

题意：给定一个数组nums，求和为k最大连续子数组长度

图解

分析

代码

class Solution {

    public int maxSubArrayLen(int[] nums, int k) {
        if (nums==null || nums.length==0) return 0;
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        map.put(0, -1);
        int sum = 0;
        int maxLen = Integer.MIN_VALUE;
        for (int i=0; i<nums.length; i++) {
            sum += nums[i];
            if (!map.containsKey(sum)) {
                map.put(sum, i);
            }
            if (map.containsKey(sum-k)) {
                int index = map.get(sum-k);
                maxLen = Math.max(maxLen, i-index);
            }
        }
        return maxLen==Integer.MIN_VALUE? 0 : maxLen;
    }
}