Question

278. 第一个错误的版本

English Version

题目描述

你是产品经理，目前正在带领一个团队开发新的产品。不幸的是，你的产品的最新版本没有通过质量检测。由于每个版本都是基于之前的版本开发的，所以错误的版本之后的所有版本都是错的。

假设你有 n 个版本 [1, 2, ..., n]，你想找出导致之后所有版本出错的第一个错误的版本。

你可以通过调用 bool isBadVersion(version) 接口来判断版本号 version 是否在单元测试中出错。实现一个函数来查找第一个错误的版本。你应该尽量减少对调用 API 的次数。

 

示例 1：

输入：n = 5, bad = 4
输出：4
解释：
调用 isBadVersion(3) -> false 
调用 isBadVersion(5) -> true 
调用 isBadVersion(4) -> true
所以，4 是第一个错误的版本。

示例 2：

输入：n = 1, bad = 1
输出：1

 

提示：

• 1 <= bad <= n <= 231 - 1

解法

方法一

# The isBadVersion API is already defined for you.
# @param version, an integer
# @return an integer
# def isBadVersion(version):


class Solution:
  def firstBadVersion(self, n):
    """
    :type n: int
    :rtype: int
    """
    left, right = 1, n
    while left < right:
      mid = (left + right) >> 1
      if isBadVersion(mid):
        right = mid
      else:
        left = mid + 1
    return left

/* 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, right = n;
    while (left < right) {
      int mid = (left + right) >>> 1;
      if (isBadVersion(mid)) {
        right = mid;
      } else {
        left = mid + 1;
      }
    }
    return left;
  }
}

// The API isBadVersion is defined for you.
// bool isBadVersion(int version);

class Solution {
public:
  int firstBadVersion(int n) {
    int left = 1, right = n;
    while (left < right) {
      int mid = left + ((right - left) >> 1);
      if (isBadVersion(mid)) {
        right = mid;
      } else {
        left = mid + 1;
      }
    }
    return left;
  }
};

/**
 * Forward declaration of isBadVersion API.
 * @param   version   your guess about first bad version
 * @return         true if current version is bad
 *            false if current version is good
 * func isBadVersion(version int) bool;
 */

func firstBadVersion(n int) int {
  left, right := 1, n
  for left < right {
    mid := (left + right) >> 1
    if isBadVersion(mid) {
      right = mid
    } else {
      left = mid + 1
    }
  }
  return left
}

// The API isBadVersion is defined for you.
// isBadVersion(version:i32)-> bool;
// to call it use self.isBadVersion(version)

impl Solution {
  pub fn first_bad_version(&self, n: i32) -> i32 {
    let mut left = 1;
    let mut right = n;
    while left < right {
      let mid = left + (right - left) / 2;
      if self.isBadVersion(mid) {
        right = mid;
      } else {
        left = mid + 1;
      }
    }
    left
  }
}

/**
 * Definition for isBadVersion()
 *
 * @param {integer} version number
 * @return {boolean} whether the version is bad
 * isBadVersion = function(version) {
 *   ...
 * };
 */

/**
 * @param {function} isBadVersion()
 * @return {function}
 */
var solution = function (isBadVersion) {
  /**
   * @param {integer} n Total versions
   * @return {integer} The first bad version
   */
  return function (n) {
    let left = 1;
    let right = n;
    while (left < right) {
      const mid = (left + right) >>> 1;
      if (isBadVersion(mid)) {
        right = mid;
      } else {
        left = mid + 1;
      }
    }
    return left;
  };
};