leetcode 374. Guess Number Higher or Lower

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374. Guess Number Higher or Lower

QuestionEditorial Solution
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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;
}
};