374. Guess Number Higher or Lower

Easy (Dễ) C++ 🔗 Xem trên LeetCode

📋 Đề Bài

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 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 three possible results:

  • -1: Your guess is higher than the number I picked (i.e. num > pick).
  • 1: Your guess is lower than the number I picked (i.e. num < pick).
  • 0: your guess is equal to the number I picked (i.e. num == pick).

Return the number that I picked.

 

Example 1:

Input: n = 10, pick = 6
Output: 6

Example 2:

Input: n = 1, pick = 1
Output: 1

Example 3:

Input: n = 2, pick = 1
Output: 1

 

Constraints:

  • 1 <= n <= 231 - 1
  • 1 <= pick <= n

💻 Lời Giải

C++ 0374-guess-number-higher-or-lower.cpp 
/** 
 * Forward declaration of guess API.
 * @param  num   your guess
 * @return 	     -1 if num is higher than the picked number
 *			      1 if num is lower than the picked number
 *               otherwise return 0
 * int guess(int num);
 */

class Solution {
public:
    int guessNumber(int n) {
        int l = 1, r = n;
        while (l <= r) {
            int m = l + (r - l) / 2;
            int c = guess(m);
            if (c == 0) {
                return m;
            } else if (c == 1) {
                l = m + 1;
            } else {
                r = m - 1;
            }
        }
        return -1;
    }
};