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Commit 0a2aaff

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# [278. 第一个错误的版本](https://leetcode-cn.com/problems/first-bad-version/description/)
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### 题目描述
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<p>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。</p>
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<p>假设你有 <code>n</code> 个版本 <code>[1, 2, ..., n]</code>,你想找出导致之后所有版本出错的第一个错误的版本。</p>
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<p>你可以通过调用&nbsp;<code>bool isBadVersion(version)</code>&nbsp;接口来判断版本号 <code>version</code> 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。</p>
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<p><strong>示例:</strong></p>
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<pre>给定 n = 5,并且 version = 4 是第一个错误的版本。
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<code>调用 isBadVersion(3) -&gt; false
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调用 isBadVersion(5)&nbsp;-&gt; true
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调用 isBadVersion(4)&nbsp;-&gt; true
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所以,4 是第一个错误的版本。&nbsp;</code></pre>
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### 解题思路
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1. 二分查找
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### 具体解法
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#### **Golang**
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```go
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func firstBadVersion(n int) int {
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l, r := 1, n
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for l < r {
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mid := (l + r) / 2
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if isBadVersion(mid) {
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r = mid
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} else {
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l = mid + 1
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}
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}
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return l
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}
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func isBadVersion(n int) bool {
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if n >= 4 {
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return true
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}
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return false
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}
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```
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package leetcode
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/*
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* @lc app=leetcode.cn id=278 lang=golang
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*
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* [278] 第一个错误的版本
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*/
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// @lc code=start
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/**
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* Forward declaration of isBadVersion API.
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* @param version your guess about first bad version
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* @return true if current version is bad
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* false if current version is good
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* func isBadVersion(version int) bool;
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*/
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func firstBadVersion(n int) int {
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l, r := 1, n
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for l < r {
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mid := (l + r) / 2
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if isBadVersion(mid) {
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r = mid
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} else {
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l = mid + 1
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}
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}
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return l
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}
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func isBadVersion(n int) bool {
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if n >= 4 {
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return true
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}
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return false
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}
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// @lc code=end
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package leetcode
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import (
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"testing"
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)
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func TestFirstBadVersion(t *testing.T) {
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var ret int
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var num int
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num = 5
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ret = 4
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if ret != firstBadVersion(num) {
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t.Fatalf("case fails %v\n", ret)
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}
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}

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