/**
 * 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 beg = 1, end = n, gap = 0
		while (beg < end) {
			if (gap == end - beg) break
			gap = end - beg
			let mid = Math.round((beg + end) / 2)
			let isBad = isBadVersion(mid)
			if (isBad) end = mid
			else if (!isBad) beg = mid + 1
		}
		if (isBadVersion(beg)) return beg
		return end
    }
}