15.first-bad-version.js

// 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 returns whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

 

// Example 1:

// Input: n = 5, bad = 4
// Output: 4
// Explanation:
// call isBadVersion(3) -> false
// call isBadVersion(5) -> true
// call isBadVersion(4) -> true
// Then 4 is the first bad version.
// Example 2:

// Input: n = 1, bad = 1
// Output: 1
 

// Constraints:

// 1 <= bad <= n <= 231 - 1
/**
 * 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 start = 1;
        let end = n;
        let mid;
        let result = mid;
        
            
        while(start <= end) {
            mid = Math.floor((start + end )/2);
            if (isBadVersion(mid)) {
                result = mid;
                end = mid - 1;
            } else {
                start = mid + 1;
            }
        }
        
        return result
    };
};