perfectSquare.js

/**
 * @param {number} num
 * @return {boolean}
 */
var isPerfectSquare = function(num) {
    if (num < 2) return true;
    
    let left = 2;
    let right = Math.floor(num / 2);
    
    while (left <= right) {
        
        let mid = left + Math.floor((right - left) / 2);
        let guess = mid * mid;
        
        if (guess === num) return true;
        
        if (guess > num) {
            right = mid - 1;
        } else {
            left = mid + 1;
        } 
    }
    return false;
};