leetcode 374. Guess Number Higher or Lower（猜数字）

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.

Example 1:

Input: n = 10, pick = 6
Output: 6

现有1～n之间的一个数字，你要去猜是哪一个，每次可以通过guess(int num)函数来确定你猜的数字跟实际数字的大小。

思路：

从升序数组1～n中找到目标数字，很明显要用到binary search.
只不过每次和目标数字比大小不是直接比，而是通过函数int guess(int num),
通过它的返回值确认现在的mid和目标数字的大小关系。

public int guessNumber(int n) {
    int left = 1;
    int right = n;
    
    while(left <= right) {
        int mid = left + (right - left) / 2;
        if(guess(mid) == 0) return mid;
        if(guess(mid) < 0) {
            right = mid - 1;
        } else {
            left = mid + 1;
        }
    }
    return left;
}
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