Contiguous subarray with 0 and 1 in JavaScript

Problem:

We are required to write a JavaScript function that takes in a binary array, arr, (an array that only consists of 0 or 1). Our function should return the length of the contiguous subarray from the array that consists of the same number of 1 and 0.

For example, if the input to the function is −

const arr = [1, 0, 0, 1, 0, 1, 0, 0];

Then the output should be −

const output = 6;

Output Explanation

The first 6 elements of the array are 1, 0, 0, 1, 0, 1 (three 1s and three 0s)

Example

The code for this will be −

 Live Demo

const arr = [1, 0, 0, 1, 0, 1, 0, 0];
const findMaxLength = (arr = []) => {
   const { length } = arr;
   if (length < 2){
      return 0
   };
   const map = new Map();
   map.set(0, -1);
   let sum = 0;
   let max = 0;
   for (var i = 0; i < length; i++) {  
      sum += arr[i] === 0 ? -1 : 1;
      if (map.has(sum)) {
         max = Math.max(max, i - map.get(sum));
      } else {
         map.set(sum, i);
      };
   };
   return max;
};
console.log(findMaxLength(arr));

Code Explanation

Here, we thought of 0 as -1 and 1 as 1, and calculated the sum for different windows, when sum is 0, we knew that subarray must have the same number of 0 and 1.

Output

And the output in the console will be −

6