Contiguous Array

Description

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.

Code

class Solution {
    //            0  1  2  3  4  5  6  7  8  9
    // int[] a = {1, 0, 0, 0, 1, 0, 0, 0, 1, 1};
    //            1  0 -1 -2 -1 -2 -3 -4 -3 -2
    public int findMaxLength(int[] nums) {
        for (int i = 0; i < nums.length; i++) {
            nums[i] = nums[i] == 0 ? -1 : nums[i];
        }

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

        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];
            if (map.containsKey(sum)) {
                max = Math.max(max, i - map.get(sum));
            } else {
                map.put(sum, i);
            }
        }
        return max;
    }
}