# (1) Binary Search: First Bad Version

 [Question Link](https://leetcode.com/problems/first-bad-version/)  and  [Solution Link](https://leetcode.com/submissions/detail/610697076/) 

**Difficulty**: Easy

**Problem Statement**: Given **n** we need to find a first bad version from 1 to n. Here we are given `bool isBadVersion(version)` this returns `true` if the version is bad and `false` if the version is good.

**Observation**: `F F F F F F T T T T T`, `T T T T T T T T`. This means once T will occur then it will occur till the end. `F F F F F T T T F F F`. This will never be the case. In simple terms, it means there will be continuous T or continuos F

**Approach**: Our correct answer will always be on the left side hence at last we will return the value of `low`.

```
int firstBadVersion(int n)
{
    int low = 1, high = n, mid;
    while (low < high)
    {
        mid = low + (high - low) / 2;
        if (isBadVersion(mid)) high = mid;
        else low = mid + 1;
    }
    return low;
}
``` 

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