1087.Brace-Expansion (prime)
package LeetCode_1087 /** * 1087.Brace-Expansion (prime) * https://leetcode.com/problems/brace-expansion/ * * A string S represents a list of words. Each letter in the word has 1 or more options. * If there is one option, the letter is represented as is. * If there is more than one option, then curly braces delimit the options. * For example, "{a,b,c}" represents options ["a", "b", "c"]. For example, "{a,b,c}d{e,f}" represents the list ["ade", "adf", "bde", "bdf", "cde", "cdf"]. Return all words that can be formed in this manner, in lexicographical order. Example 1: Input: "{a,b}c{d,e}f" Output: ["acdf","acef","bcdf","bcef"] Example 2: Input: "abcd" Output: ["abcd"] Note: 1. 1 <= S.length <= 50 2. There are no nested curly brackets. 3. All characters inside a pair of consecutive opening and ending curly brackets are different. * */ class Solution { /* * solution: DFS, Time:O(2^n), Space:O(n) * 1. create list format, for example:{a,b}c{d,e}f => [[a,b], [c], [d, e]] * 2. dfs to create result * */ fun expand(s: String): Array<String?> { val result = ArrayList<String>() val lists = ArrayList<ArrayList<String>>() var i = 0 var j = 0 while (i < s.length) { val c = s[i] if (c != '{') { //is letter, append it lists.add(ArrayList(listOf(c.toString()))) } else { //keep track to find out all letter j = i while (j < s.length && s[j] != '}') { j++ } val rString = s.substring(i + 1, j) val rList = rString.split(",") rList.sorted() lists.add(ArrayList(rList)) //move the i to right i = j } i++ } dfs(0, StringBuilder(), lists, result) //set for result val arrays = arrayOfNulls<String>(result.size) for (i in result.indices) { arrays[i] = result[i] } return arrays } private fun dfs(index: Int, sb: StringBuilder, lists: ArrayList<ArrayList<String>>, res: ArrayList<String>) { //if enumerated all element in lists, add into res if (index == lists.size) { res.add(sb.toString()) return } for (str in lists[index]) { sb.append(str) dfs(index + 1, sb, lists, res) //for next level sb.setLength(sb.length - 1) } } }