sqrtx.js

/**
 * @param {number} x
 * @return {number}
 */

var mySqrt = function(x) {

    let left = 1;
    let right = x;
    
    // The square root of 0 or 1 is itself
    
    if(x < 2) 
        return x;

    // Use binary search to find the square root or the whole number closest to the square root
    
    while(left < right) {
        
        // Find the mid point between left and right
        
        const mid = Math.floor((left + right) / 2)
        
        // Return the mid point if this is the square root
        
        if(mid*mid === x) 
            return mid;
        
        // If mid squared is greater than x then the answer must be on the left half of mid
        
        else if(mid*mid >x) 
            right = mid;
       
        // If mid squred is less than x then the answer must be on the right half of mid
        
        else 
            left = mid+1;
    }
    
    return left - 1;
    
};