[LeetCode] 139. Word Break

Given a binary array, find the maximum length of a contiguous subarray with equal number of 0 and 1.

Example 1:

Input: [0,1]
Output: 2
Explanation: [0, 1] is the longest contiguous subarray with equal number of 0 and 1.

 

Example 2:

Input: [0,1,0]
Output: 2
Explanation: [0, 1] (or [1, 0]) is a longest contiguous subarray with equal number of 0 and 1.

 

Note: The length of the given binary array will not exceed 50,000.

题意，统计最长的子序列，其中0和1的个数相同，

统计每个位子的和，把0看做-1即可

class Solution {
    public int findMaxLength(int[] nums) {
        Map<Integer, Integer> map = new HashMap<>();
        map.put(0, -1);
        int sum = 0;
        int max = 0;
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] == 0)
                nums[i] = -1;
            sum += nums[i];
            if (map.containsKey(sum)) {
                max = Math.max(max, i - map.get(sum));
            } else {
                map.put(sum, i);
            }
        }
        return max;
    }
}