guess-number-higher-or-lower.js

/* Guess Number Higher or Lower

We are playing the Guess Game. The game is as follows:
I pick a number from 1 to n. You have to guess which number I picked.

Every time you guess wrong, I will tell you whether the number I picked is higher or lower than your guess.

You call a pre-defined API int guess(int num), which returns 3 possible results:
    -1: The number I picked is lower than your guess (i.e. pick < num).
    1: The number I picked is higher than your guess (i.e. pick > num).
    0: The number I picked is equal to your guess (i.e. pick == num).

Return the number that I picked.

Example 1:
Input: n = 10, pick = 6
Output: 6

Example 2:
Input: n = 1, pick = 1
Output: 1

Example 3:
Input: n = 2, pick = 1
Output: 1

Example 4:
Input: n = 2, pick = 2
Output: 2

Constraints:
    1 <= n <= 231 - 1
    1 <= pick <= n
 */

/** 
 * Forward declaration of guess API.
 * @param {number} num   your guess
 * @return 	            -1 if num is lower than the guess number
 *			             1 if num is higher than the guess number
 *                       otherwise return 0
 * var guess = function(num) {}
 */

/**
 * @param {number} n
 * @return {number}
 */
 var guessNumber = function(n) {
    let left = 1, right = n;

    while(left <= right){
        let mid = Math.floor(left+(right-left)/2);
        let g = guess(mid);
        if(g === 0){
            return mid;
        }else if(g < 0){
            right  = mid - 1;
        }else{
            left  = mid + 1;
        }
    }
    return -1
};