[LeetCode] 374. Guess Number Higher or Lower 猜數字大小

 

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.

 

這道題是一道典型的猜價格的問題，根據對方說高了還是低了來縮小范圍，雖然是道 Easy 題，無腦線性遍歷還是會超時 Time Limit Exceeded，所以更快速的方法就是折半搜索法，原理很簡單，屬於博主之前的總結帖 LeetCode Binary Search Summary 二分搜索法小結 中的第四類-用子函數當作判斷關系，參見代碼如下：

 

int guess(int num);

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

 

Github 同步地址：

https://github.com/grandyang/leetcode/issues/374

 

類似題目：

Guess Number Higher or Lower II 

First Bad Version

Find K Closest Elements

 

參考資料：

https://leetcode.com/problems/guess-number-higher-or-lower/

https://leetcode.com/problems/guess-number-higher-or-lower/discuss/84664/0ms-c%2B%2B-binary-search

 

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