LeetCode - Easy - 278

Suppose you have n versions [1, 2, ..., n] and you want to find out the first bad one, which causes all the following ones to be bad.

You are given an API bool isBadVersion(version) which returns whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

Example 1:

Input: n = 5, bad = 4

Output: 4

Explanation:

call isBadVersion(3) -> false

call isBadVersion(5) -> true

call isBadVersion(4) -> true

Then 4 is the first bad version.

Example 2:

Input: n = 1, bad = 1

Output: 1

Constraints:

• 1 <= bad <= n <= 2³¹ - 1

Analysis

---

略

Submission

---

class VersionControl{

public static int badVersion;

public boolean isBadVersion(int version) {

return version >= badVersion;

}

}

public class FirstBadVersion extends VersionControl{

public int firstBadVersion(int n) {

int left = 1, right = n;

while(left < right) {

int mid = left + (right - left) / 2;

if(isBadVersion(mid)) {

right = mid;

}else {

left = mid + 1;

}

}

return right;

}

}

Test

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import static org.junit.Assert.*;

import org.junit.Test;