LeetCode #374 Guess Number Higher or Lower Solution & Explanation

LeetCode Problem

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

Solution

After reading this question, I realized that it is very similar to another question – LeetCode #278 First Bad Version. The only difference is that one uses integers and the other returns a boolean.

Therefore, we can use binary search to easily solve this question with O(log n) time complexity.

C# Solution

Solution1

/** 
 * 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);
 */

public class Solution : GuessGame {
    public int GuessNumber(int n) {
        int max =n;
        int min =1;

        while(min<=max)
        {
            n = min+(max-min)/2;
            var chk = guess(n);
            if(chk == -1)
            {
                max = n-1;
            }
            else if(chk == 0){
                return n;
            }
            else
            {
                min = n+1;
            }
        }
        return -1;
    }
}

Conclusion

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The problem link : Guess Number Higher or Lower – LeetCode

Similar Questions(binary search)

• LeetCode #34 Find First and Last Position of Element in Sorted Array Solution & Explanation
• LeetCode #35 Search Insert Position Solution & Explanation
• LeetCode #278 First Bad Version Solution & Explanation

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