leetcode 374. Guess Number Higher or Lower

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374. Guess Number Higher or Lower

 

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• 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

 

 

// 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 l = 1,r = n;
        int mid = (l + r) / 2;
        while(l < r){
            mid = l + (r - l) / 2;
            int re = guess(mid);
            if(re == 0) return mid;
            else if(re == 1){
                l = mid + 1;
            }
            else{
                r = mid - 1;
            }
        }
        return l;
    }
};