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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 = 6Output: 6

Example 2:

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

Example 3:

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

Example 4:

Input: n = 2, pick = 2Output: 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

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