278_first_bad_version.java

/* 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;
        int ans = -1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (isBadVersion(mid) == true) {
                if (isBadVersion(mid-1) == false) {
                    ans = mid;
                    break;
                } else {
                    right = mid - 1;
                }
            } else {
                if (isBadVersion(mid+1) == true) {
                    ans = mid + 1;
                    break;
                } else {
                    left = mid + 1;
                }
            }
        }
        return ans;
    }
}

/**
 * This is my personal record of solving Leetcode Problems. 
 * If you have any questions, please discuss them in [Issues](https://github.com/mengxinayan/leetcode/issues).
 * Copyright (C) 2020-2022  mengxinayan
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */