[374]Guess Number Higher or Lower

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本文介绍了一种通过二分搜索解决猜数字游戏的方法。玩家需要从1到n中猜出预设的数字，每次猜测都会得到反馈：数字偏高、偏低还是正确。文章详细解释了如何使用二分搜索算法来高效地找到正确答案。

【题目描述】

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.

【解题思路】

二分搜索

【代码】

// Forward declaration of guess API.
// @param num, your guess
// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num);

class Solution {
public:
    int guessNumber(int n) {
        int low=1;
        int high=n;
        int mid;
        int ans=-1;
        while(1){
            mid=(high-low)/2+low;
            if(guess(mid)==0){
                ans=mid;
                break;
            }
            else if(guess(mid)==1){
                low=mid+1;
            }
            else if(guess(mid)==-1){
                high=mid-1;
            }
            
        }
        return ans;
    }
};