525. Contiguous Array Leetcode Problem Java

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

Constraints:

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

Hint: Use Hashmap to keep track of sum at each index if array value is 0 then add -1 else add 1.

Get Soham’s stories in your inbox

Join Medium for free to get updates from this writer.

Remember me for faster sign in

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.

Solution:

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