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.

class Solution {
    public int findMaxLength(int[] nums) {
        if (nums == null || nums.length == 0) return 0;

        for (int i = 0; i < nums.length; i++){
            if (nums[i] == 0) nums[i] = -1;
        }

        int sum = 0, ans = 0;
        Map<Integer, Integer> hash = new HashMap<>();
        hash.put(0, -1);

        for (int i = 0; i < nums.length; i++){
            sum += nums[i];

            if (hash.containsKey(sum)){
                int range = i - hash.get(sum);
                ans = Math.max(ans, range);
            }
            else{
                hash.put(sum, i);
            }
        }

        return ans;
    }
}