LeetCode 278: First Bad Version Solution

Master LeetCode problem 278 (First Bad Version), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

278. First Bad Version

Easy

Binary Search Interactive

Problem Explanation

Explanation

To find the first bad version, we can use binary search as it allows us to minimize the number of calls to the API. We start by setting two pointers, left and right, to the first and last versions respectively. Then, we continuously check the middle version using the isBadVersion API and adjust the pointers accordingly based on whether the middle version is bad or not. We keep dividing the search space in half until we find the first bad version.

Initialize left = 1 and right = n
While left < right:
- Calculate the middle version as mid = left + (right - left) / 2
- If isBadVersion(mid) returns true:
  - Update right = mid
- Else:
  - Update left = mid + 1
Return left as the first bad version

Time Complexity

The time complexity of this approach is O(log n) as we are reducing the search space by half in each iteration of the binary search.

Space Complexity

The space complexity is O(1) as we are using a constant amount of extra space.

Solution Code

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int left = 1;
        int right = n;
        while (left < right) {
            int mid = left + (right - left) / 2;
            if (isBadVersion(mid)) {
                right = mid;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }
}

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