[leetcode] 374. Guess Number Higher or Lower

Question:

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’ll tell you whether the number is higher or lower.

You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0):-1 : My number is lower 1 : My number is higher 0 : Congrats! You got it!Example:n = 10, I pick 6.Return 6.

Solution:

简单的二分。注意类型用long long，因为测试数据会非常大。
时间复杂度：O（logn）
空间复杂度：O（1）

// Forward declaration of guess API.// @param num, your guess// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0int guess(int num);class Solution {public:    int guessNumber(int n) {        long long l = 1, r = n;        while (l <= r) {            long long mid = (l + r) / 2;            int tmp = guess(mid);            if (tmp == 0) return mid;            if (tmp == 1)                l = mid + 1;            else                r = mid-1;        }        return -1;    }};