525. Contiguous Array

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

 

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.