LeetCode in Kotlin
3211. Generate Binary Strings Without Adjacent Zeros
Medium
You are given a positive integer n.
A binary string x is valid if all substrings of x of length 2 contain at least one "1".
Return all valid strings with length n, in any order.
Example 1:
Input: n = 3
Output: [“010”,”011”,”101”,”110”,”111”]
Explanation:
The valid strings of length 3 are: "010", "011", "101", "110", and "111".
Example 2:
Input: n = 1
Output: [“0”,”1”]
Explanation:
The valid strings of length 1 are: "0" and "1".
Constraints:
1 <= n <= 18
Solution
class Solution {
fun validStrings(n: Int): List<String> {
val strings: MutableList<String> = ArrayList()
dfs(n, StringBuilder(), strings)
return strings
}
private fun dfs(n: Int, build: StringBuilder, strings: MutableList<String>) {
if (build.length == n) {
strings.add(build.toString())
return
}
// need to add a one
if (build.isNotEmpty() && build[build.length - 1] == '0') {
build.append('1')
dfs(n, build, strings)
// undo for backtracking
build.setLength(build.length - 1)
return
}
// choose to append a one
build.append('1')
dfs(n, build, strings)
build.setLength(build.length - 1)
// choose to append a zero
build.append('0')
dfs(n, build, strings)
build.setLength(build.length - 1)
}
}