guessNumberHigherorLower.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
/**
 * 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}
 */
 const guessNumber = function(n) {
    let left = 0, right = n;

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

    return 0;
};

// console.log(guessNumber(10));
// console.log(guessNumber(1));
// console.log(guessNumber(2));