278.first-bad-version.java

/*
 * @lc app=leetcode id=278 lang=java
 *
 * [278] First Bad Version
 *
 * https://leetcode.com/problems/first-bad-version/description/
 *
 * algorithms
 * Easy (28.99%)
 * Total Accepted:    215.1K
 * Total Submissions: 727.9K
 * Testcase Example:  '5\n4'
 *
 * You are a product manager and currently leading a team to develop a new
 * product. Unfortunately, the latest version of your product fails the quality
 * check. Since each version is developed based on the previous version, all
 * the versions after a bad version are also bad.
 *
 * 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 will return whether
 * version is bad. Implement a function to find the first bad version. You
 * should minimize the number of calls to the API.
 *
 * Example:
 *
 *
 * Given n = 5, and version = 4 is the first bad version.
 *
 * call isBadVersion(3) -> false
 * call isBadVersion(5) -> true
 * call isBadVersion(4) -> true
 *
 * Then 4 is the first bad version. 
 *
 */
/* 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 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;
  }
}