Topic
- Binary Search
Description
https://leetcode.com/problems/guess-number-higher-or-lower/
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 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.
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
Example 4:
Input: n = 2, pick = 2
Output: 2
Constraints:
- 1 <= n <= 2³¹ - 1
- 1 <= pick <= n
Analysis
略
Submission
class GuessGame {
public static int pick;
public int guess(int num) {
return pick == num ? 0 : pick < num ? -1 : 1;
}
}
public class GuessNumberHigherOrLower extends GuessGame {
public int guessNumber(int n) {
int left = 1, right = n;
while (left <= right) {
int mid = left + (right - left) / 2;
int guess = guess(mid);
if (guess < 0)
right = mid - 1;
else if (guess > 0)
left = mid + 1;
else
return mid;
}
return -1;
}
}
Test
import static org.junit.Assert.*;
import org.junit.Test;
public class GuessNumberHigherOrLowerTest {
@Test
public void test() {
GuessNumberHigherOrLower obj = new GuessNumberHigherOrLower();
assertEquals(GuessGame.pick = 6, obj.guessNumber(10));
assertEquals(GuessGame.pick = 1, obj.guessNumber(1));
assertEquals(GuessGame.pick = 1, obj.guessNumber(2));
assertEquals(GuessGame.pick = 2, obj.guessNumber(2));
}
}