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.

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