Recursion Day 11 is Completed

pradeepkumar24rk · pradeepkumar24rk · commit ff22ed274282 · 2024-07-09T18:21:23.000+05:30
diff --git a/Recursion/LetterCombination.java b/Recursion/LetterCombination.java
@@ -1,20 +1,51 @@
 package Recursion;
 
+import java.util.ArrayList;
+import java.util.List;
+
 public class LetterCombination {
 
-    private static void pad(String str,String ans) {
-        if(str.length()==0) {
+    private static void pad(String str, String ans) {
+        if (str.length() == 0) {
             System.out.println(ans);
             return;
         }
-        
+
+        int digit = str.charAt(0) - '0';
+        for (int i = (digit - 1) * 3; i < (digit * 3); i++) {
+            char ch = (char) ('a' + i);
+            pad(str.substring(1), ans + ch);
+        }
+    }
+
+    static List<String> padleetcode(String str, String ans) {
+
+        if (str.length() == 0) {
+            ArrayList<String> list = new ArrayList<>();
+            list.add(ans);
+            return list;
+        }
         int digit = str.charAt(0) - '0';
-        for(int i = (digit-1)*3;i<(digit*3);i++) {
-            char ch = (char) ('a'+i);
-            pad(str.substring(1), ans+ch);
+        ArrayList<String> mainlist = new ArrayList<>();
+        int s = (digit - 2) * 3, e = ((digit - 1) * 3);
+        if (digit == 7)
+            e += 1;
+        else if (digit == 8) {
+            s += 1;
+            e += 1;
+        } else if (digit == 9) {
+            s += 1;
+            e += 2;
         }
+        for (int i = s; i < e; i++) {
+            char ch = (char) ('a' + i);
+            mainlist.addAll(padleetcode(str.substring(1), ans + ch));
+        }
+        return mainlist;
     }
+
     public static void main(String[] args) {
-        pad("12", "");
+        pad("18", ""); // 1-8 (9-yz)
+        System.out.println(padleetcode("29", "")); // 2-9 (7 - pqrs, 8 - tuv, 9 - wxyz)
     }
 }
diff --git a/Recursion/Permutations.java b/Recursion/Permutations.java
@@ -1,6 +1,7 @@
 package Recursion;
 
 import java.util.ArrayList;
+import java.util.List;
 
 public class Permutations {
 
@@ -49,11 +50,30 @@ private static int permutationCount(String str,String ans) {
         return count;
     }
     
+// Array Permutation
+    static void permutationArray(int[] nums,List<List<Integer>> list,List<Integer> ans,int index) {
+        if(index == nums.length){
+            list.add(ans);
+            return;
+        }
+        for(int i = 0;i<=ans.size();i++){
+            List<Integer> temp = new ArrayList<>(ans) ;
+            temp.add(i,nums[index]);
+            permutationArray(nums,list,temp,index+1);
+        }
+    }
+    public static List<List<Integer>> Arraypermute(int[] nums) {
+        List<List<Integer>> list = new ArrayList<>();
+        permutationArray(nums,list,new ArrayList<Integer>(),0);
+        return list;
+    }
+    
     public static void main(String[] args) {
         String str = "abc";
         permutation(str,"");
         System.out.println(permutationArrayList(str,""));
         System.out.println(permutationCount("abcd",""));
+        System.out.println(Arraypermute(new int[] {1,2,3}));
         
     }
 }
