[Leetcode] 374. Guess Number Higher or Lower 解题报告

原创于 2017-08-25 09:55:47 发布 · 259 阅读

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本文介绍了一个基于二分查找的经典猜数字游戏算法实现。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以调整下一次猜测的方向。通过二分查找的方法可以在最短的步骤内找到正确答案。

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题目：

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.

思路：

最基本的二分查找，一定要闭着眼睛都能写出来^_^。

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