LeetCode 374. Guess Number Higher or Lower【二分】简单

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

题意：猜数字游戏。

---

解法 二分

/** 
 * Forward declaration of guess API.
 * @param  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
 * int guess(int num);
 */
class Solution {
public:
    int guessNumber(int n) {
        int l = 0, h = n;
        while (l <= h) {
            int m = l + (h - l) / 2, t = guess(m);
            if (t == 0) return m;
            else if (t == -1) h = m - 1;
            else l = m + 1; 
        }
        return 0;
    }
};

运行效率如下：

执行用时：0 ms, 在所有 C++ 提交中击败了100.00% 的用户
内存消耗：5.7 MB, 在所有 C++ 提交中击败了82.14% 的用户