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 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.
//
//
// Credits:Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.


/**
 * 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) {
        var start = 1;
        var end = n;
        while(start + 1 < end) {
            var center = parseInt(((end - start) / 2) + start);
            if (isBadVersion(center)) {
                end = center;
            } else {
                start = center;
            }

        }
        if (isBadVersion(start)) {
            return start;
        }
        return end;
    };
};