525. Contiguous Array

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.

本题和maximun size subarray sum equal k比较类似，这里有一个把0转换成-1来进行计算的过程，然后存储一个hashmap用来存放sum，如果接下来的sum在hashmap里面出现过，则说明hashmap里面出现的那个值的索引的开始（不包括索引），到目前的索引的和为0，代码如下：

public class Solution {
    public int findMaxLength(int[] nums) {
        Map<Integer,Integer> map = new HashMap<Integer,Integer>();
        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;
    }
}