firstBadVersion.js

////////////////////////////////////////////////First Bad Version///////////////////////////////////////////
// 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
/**
 * Definition for isBadVersion()
 *
 * @param {integer} version number
 * @return {boolean} whether the version is bad
 * isBadVersion = function(version) {
 *     ...
 * };
 */

/**
 * @param {function} isBadVersion()
 * @return {function}
 */
 const solution = function(isBadVersion) {
    /**
     * @param {integer} n Total versions
     * @return {integer} The first bad version
     */
    return function(n) {
        let r = n, l = 0;
        while(l <= r){
            let mid = Math.floor((l + r) / 2);
            let version = isBadVersion(mid);
            if(version !== isBadVersion(mid + 1)){
                return mid + 1
            }else if(version === false){
                l = mid + 1
            }else{
                r = mid - 1
            }
        }
    };
};