278. First Bad Version

问题链接：https://leetcode.com/problems/first-bad-version/?tab=Description

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.

采用二分查找法，可将查找次数降至Logn

/* 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 start = 1, end = n;        while(start < end) {            int mid = start + (end - start)/2;            if(isBadVersion(mid))                end = mid;            else                start = mid+1;        }        return start;    }}

开始时采用递归方式，但是造成栈溢出

Submission Result: Runtime Error More Details 

Runtime Error Message:Line 20: java.lang.StackOverflowError

Last executed input:2126753390 versions1702766719 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) {        return find(1,n);    }        private int find(int left, int right) {        int mid = (left + right) / 2;        if(isBadVersion(mid)) {            if(!isBadVersion(mid-1))                return mid;            else                find(left,mid);        } else {            if(isBadVersion(mid+1))                return mid+1;            else                find(mid+1,right);        }        return 0;    }}