374. Guess Number Higher or Lower

 

QuestionEditorial Solution

 

 

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• 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 };