
# First Bad Version

## Description

[doc](https://leetcode.com/problems/first-bad-version/)

## Solutions

### First Idea

```javascript
/**
 * 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 low = 1
    let high = n

    while (low <= high) {
      const middle = low + Math.floor((high - low) / 2)
      if (low === middle) {
        return isBadVersion(low) ? low : low + 1
      }

      isBadVersion(middle) ? (high = middle) : (low = middle)
    }

    return -1
  }
}
```

- Time Complexity: O(logn)
- Space Complexity: O(1)
