First Bad Version

First Bad Version

https://leetcode.com/problems/first-bad-version/

Tips

见本章首页

Code

/* The isBadVersion API is defined in the parent class VersionControl.
      boolean isBadVersion(int version); */

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int start = 0, end = n;
        while (start < end) {
            int mid = start + (end - start) / 2;
            if (!isBadVersion(mid)) {
                start = mid + 1; 
            } else {
                end = mid;
            }
        }

        return start;
    }
}

Analysis

O(lgn)