Leetcode-Guess Number Higher Or Lower

LeetCode

發布日期: 2022-06-13

🌿 難度：Easy

🌿 題目

我們正在玩猜數字遊戲，規則如下:

We are playing the Guess Game. The game is as follows:

我在 1 到 n 中選定一個數字，你必須猜中我所指定的數字。
每當你猜錯時，我將告訴你，你猜的數字比指定數字高還是低。

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.

你將呼叫一個預定義的整數猜測 API（整數），此 API 會回傳三種結果

-1: 你猜的數字高於指定數字
1: 你猜的數字低於指定數字
0: 你猜的數字等於指定數字

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).

最後回傳指定數字

Return the number that I picked.

限制：

1 <= n <= $2^{31}$ - 1
1 <= pick <= n

Constraints:
1 <= n <= $2^{31}$ - 1
1 <= pick <= n

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

🌿 解題

/** 
 * 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 start = 1;
    let end = n;
    
    while(start <= end) {
        let mid = start + Math.floor((end-start)/2)
        
        if (guess(mid) === 0){
            return mid
        } else if(guess(mid) === 1) {
            start = mid+1
        } else {
            end = mid-1
        }
    }
};