374.Guess-Number-Higher-or-Lower.js

// 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 three possible results:
// -1: Your guess is higher than the number I picked (i.e. num > pick).
// 1: Your guess is lower than the number I picked (i.e. num < pick).
// 0: your guess is equal to the number I picked (i.e. num == pick).
// Return the number that I picked.

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

/**
 * @param {number} n
 * @return {number}
 */
var guessNumber = function(n) {
    let l = 1;
    let r = n;
    let num = (l + r) / 2;
    let g = guess(num);
    while (g != 0) {
        if (g == 1) {
            l = num;
        } else {
            r = num;
        }
        num = (l + r) / 2;
        g = guess(num);
    }
    return num;
};