525. Contiguous Array

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Problem

Given a binary array nums, return the maximum length of a contiguous subarray with an equal number of 0 and 1.

Example 1:

Input: nums = [0,1]
Output: 2
Explanation: [0, 1] is the longest contiguous subarray with an equal number of 0 and 1.

Example 2:

Input: nums = [0,1,0]
Output: 2
Explanation: [0, 1] (or [1, 0]) is a longest contiguous subarray with equal number of 0 and 1.

Constraints:

• 1 <= nums.length <= 10^5
• nums[i] is either 0 or 1.

Code

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