ContiguousSubArray.java

class Solution {
    public int findMaxLength(int[] nums) {
        int maxLen = 0;
        int sum = nums.length;
        int[] prevSums = new int[2 * nums.length + 1];
        for (int i = 0; i < prevSums.length; i++) {
            prevSums[i] = -2;
        }
        prevSums[nums.length] = -1;
        for (int i = 0;  i < nums.length; i++) {
            sum += (nums[i] * 2 - 1);
            if (prevSums[sum] == -2) {
                prevSums[sum] = i;
            } else {
                maxLen = Math.max(maxLen, i - prevSums[sum]);
            }
        }
        return maxLen;
    }
}