题目描述
题目链接:374. Guess Number Higher or Lower
We are playing the Guess Game. The game is as follows:
I pick a number from
1
ton
. You have to guess which number I picked.Every time you guess wrong, I will tell you whether the number I picked is higher or lower than your guess.
You call a pre-defined API
int guess(int num)
, which returns 3 possible results:
-1
: The number I picked is lower than your guess (i.e.pick < num
).1
: The number I picked is higher than your guess (i.e.pick > num
).0
: The number I picked is equal to your guess (i.e.pick == num
). Return the number that I picked.
例子
例子 1
Input:
n = 10, pick = 6
Output:6
例子 2
Input:
n = 1, pick = 1
Output:1
例子 3
Input:
n = 2, pick = 1
Output:1
Constraints
1 <= n <= 2^31 - 1
1 <= pick <= n
解题思路
在给定范围内猜一个数,用简单的二分查找即可。每次猜错时表明中间数不在搜索范围,因此收缩左/右边界时应该收缩到中间值右/左移一位。代码如下:
/**
* Forward declaration of guess API.
* @param num your guess
* @return -1 if num is lower than the guess number
* 1 if num is higher than the guess number
* otherwise return 0
* int guess(int num);
*/
class Solution {
public:
int guessNumber(int n) {
int left = 1;
int right = n;
while (left < right) {
int mid = ((long)left + right) / 2;
if (guess(mid) == 0) {
return mid;
} else if (guess(mid) == 1) {
left = mid + 1;
} else {
right = mid - 1;
}
}
return left;
}
};
- 时间复杂度:
O(log n)
- 空间复杂度:
O(1)
GitHub 代码同步地址: 374.GuessNumberHigherOrLower.cpp
其他题目: GitHub: Leetcode-C++-Solution 博客: Leetcode-Solutions