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.
Algorithm:
 Initialize two variables
curSum
andmax
 Loop through the array and increment
curSum
by 1 if nums[i] is 1 else decrement 1 
Now you can encounter two cases

Sub array formed from index 0
In this case just take the current index and add 1
In above examples it would be 1+1 = 2 for 1st example and 3+1 = 4 for 2nd example

Sub Array formed after index 0
In this scenario you have to find the previous index of cursum and subtract it
In above image it would be 51 = 4

Here's the Code:
/**
* @param {number[]} nums
* @return {number}
*/
var findMaxLength = function(nums) {
let curSum = 0, max =0;
let map = new Map();
for(let i = 0; i < nums.length; i++) {
if(nums[i] == 0) {
curSum;
} else {
curSum++;
}
if(curSum == 0) {
max = i + 1
}
if(map.has(curSum)) {
max = Math.max(max, i  map.get(curSum))
} else {
map.set(curSum, i)
}
}
return max;
};
You can optimize the if condition where curSum == 0 by adding a value into map {0: 1}
Now, in the condition map.has(curSum), it will be something like 1  (1) = 2
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