leetcode-solutions/278.first-bad-version.cpp at master · Raees678/leetcode-solutions · GitHub

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/*
 * @lc app=leetcode id=278 lang=cpp
 *
 * [278] First Bad Version
 *
 * https://leetcode.com/problems/first-bad-version/description/
 *
 * algorithms
 * Easy (27.60%)
 * Likes:    852
 * Dislikes: 490
 * Total Accepted:    272.6K
 * Total Submissions: 850K
 * 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.
 *
 *
 */

// @lc code=start
// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
 public:
  int firstBadVersion(int n) {
    int low = 1;
    int high = n;

    while (low <= high) {
      int mid = low + (high - low) / 2;
      bool is_bad = isBadVersion(mid);
      if (!is_bad) {
        low = mid + 1;
      } else if (is_bad && isBadVersion(mid - 1)) {
        high = mid - 1;
      } else {
        return mid;
      }
    }

    return -1;
  }
};
// @lc code=end