Improved task 1415.

Author: javadev

src/main/java/g1401_1500/s1415_the_k_th_lexicographical_string_of_all_happy_strings_of_length_n/Solution.java

@@ -1,40 +1,36 @@
 package g1401_1500.s1415_the_k_th_lexicographical_string_of_all_happy_strings_of_length_n;
 
-// #Medium #String #Backtracking #2022_03_26_Time_2_ms_(89.96%)_Space_40.8_MB_(91.57%)
+// #Medium #String #Backtracking #2022_03_27_Time_2_ms_(90.55%)_Space_42.5_MB_(65.75%)
 
 public class Solution {
- public String getHappyString(int n, int k) {
- int finalLength = (int) (3 * Math.pow(2, n - 1));
- StringBuilder res = new StringBuilder();
- if (k > finalLength) {
- return "";
+ private char[] arr = new char[] {'a', 'b', 'c'};
+ private String res = "";
+ private int k;
+
+ private void get(StringBuilder str, int n, int index) {
+ if (k < 1) {
+ return;
+ }
+ if (str.length() == n) {
+ if (k == 1) {
+ res = str.toString();
+ }
+ k--;
+ return;
  }
- k--;
- int previousCall = -1;
- int calls = 3;
- for (int i = 0; i < n; i++) {
- int parts = finalLength / calls;
- int currentCall = k / parts;
- if (currentCall == 0) {
- if (previousCall == 0) {
- previousCall = 1;
- } else {
- previousCall = 0;
- }
- } else if (currentCall == 1) {
- if (previousCall == -1 || previousCall == 2) {
- previousCall = 1;
- } else {
- previousCall = 2;
- }
- } else {
- previousCall = 2;
+ for (int i = 0; i < 3; i++) {
+ if (i == index) {
+ continue;
  }
- calls = 2;
- res.append((char) ('a' + previousCall));
- finalLength = parts;
- k -= (currentCall * parts);
+ str.append(arr[i]);
+ get(str, n, i);
+ str.deleteCharAt(str.length() - 1);
  }
- return res.toString();
+ }
+
+ public String getHappyString(int n, int k) {
+ this.k = k;
+ get(new StringBuilder(), n, -1);
+ return res;
  }
 }