leetcode 374. Guess Number Higher or Lower-优快云博客

本文介绍了一种简单有效的猜数字游戏算法实现。采用二分查找法，在每轮猜测中缩小范围，直至找到正确答案。文章提供了C++代码示例，并强调了避免整数溢出的方法。

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374. Guess Number Higher or Lower

QuestionEditorial Solution

My Submissions

Total Accepted: 6632
Total Submissions: 21010
Difficulty: Easy

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.


题解：
简单的二分，需要注意：

用
mid = l + (r - l) / 2;
不要用
mid = (l + r) / 2;
会溢出

 1 // Forward declaration of guess API.
 2 // @param num, your guess
 3 // @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
 4 int guess(int num);
 5 
 6 class Solution {
 7 public:
 8     int guessNumber(int n) {
 9         int l = 1,r = n;
10         int mid = (l + r) / 2;
11         while(l < r){
12             mid = l + (r - l) / 2;
13             int re = guess(mid);
14             if(re == 0) return mid;
15             else if(re == 1){
16                 l = mid + 1;
17             }
18             else{
19                 r = mid - 1;
20             }
21         }
22         return l;
23     }
24 };