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.

Examples

Example 1:

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

Example 2:

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

Example 3:

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

Solution

Method 1 - Binary Search 🏆

This is a typical binary search problem.

Code

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public int guessNumber(int n) {
	int low = 1;
	int high = n;

	while (low<= high) {
		int mid = low + ((high - low) / 2);
		int result = guess(mid);
		if (result == 0) {
			return mid;
		} else if (result == 1) {
			low = mid + 1;
		} else {
			high = mid - 1;
		}
	}

	return -1;
}

What We Learn From This Problem?

Avoid Overflow when calculating Mid in Binary Search