525. Contiguous Array

 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 <= 105
• nums[i] is either 0 or 1.

class Solution {

public:

    

    int findMaxLength(vector<int>& nums) {

        unordered_map<int, int> mp;

        mp[0] = -1;

        int ans = 0;

        int counter = 0;

        for (int i = 0; i < nums.size(); i++) {

            if (nums[i] == 1) {

                counter++;

            } else {

                counter--;

            }

            if (mp.count(counter) != 0) {

                ans = max(ans, i - mp[counter]);

            } else {

                mp[counter] = i;

            }

        }

        return ans;

    }

};