LeetCode #374: Guess Number Higher or Lower (C/C++).

easy

source: https://leetcode.com/problems/guess-number-higher-or-lower
C/C++ Solution to LeetCode problem 374. Guess Number Higher or Lower.

Problem

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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.

Examples

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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

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• 1 <= n <= 231 - 1
• 1 <= pick <= n

Solution

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/** 
 * 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) {
    long long l = 0;
    long long h = n;
    int m, g;

    while (l <= h) {
      m = (int)((l + h) / 2);
      g = guess(m);
      
      if (g == 0)
        break;
      if (g == -1)
        h = m - 1;
      if (g == 1)
        l = m + 1;
    }

    return m;
  }
};