some advanced recursion questions

binodcoder · binodcoder · commit 5f6a32e56121 · 2024-05-27T11:27:19.000+01:00
diff --git a/src/binod/CountPaths.java b/src/binod/CountPaths.java
@@ -0,0 +1,21 @@
+package binod;
+public class CountPaths {
+    public static int countPaths(int i, int j, int n, int m) {
+        if (i == n || j == m) {
+            return 0;
+        }
+        if (i == n - 1 && j == m - 1) {
+            return 1;
+        }
+        //move downwords
+        int downPaths = countPaths(i + 1, j, n, m);
+        //move right
+        int rightPaths = countPaths(i, j + 1, n, m);
+        return downPaths + rightPaths;
+    }
+    public static void main(String[] args) {
+        int n = 3, m = 3;
+        int totalPaths = countPaths(0, 0, n, m);
+        System.out.println(totalPaths);
+    }
+}
diff --git a/src/binod/KeyPad.java b/src/binod/KeyPad.java
@@ -0,0 +1,19 @@
+package binod;
+public class KeyPad {
+    public static String[] keypad = {".", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tu", "vwx", "yz"};
+    public static void printComb(String str, int idx, String combination) {
+        if (idx == str.length()) {
+            System.out.println(combination);
+            return;
+        }
+        char currChar = str.charAt(idx);
+        String mapping = keypad[currChar - '0'];
+        for (int i = 0; i < mapping.length(); i++) {
+            printComb(str, idx + 1, combination + mapping.charAt(i));
+        }
+    }
+    public static void main(String[] args) {
+        String str = "23";
+        printComb(str, 0, "");
+    }
+}
diff --git a/src/binod/PrintPermutations.java b/src/binod/PrintPermutations.java
@@ -0,0 +1,19 @@
+package binod;
+public class PrintPermutations {
+    public static void printPerm(String str, String permutation) {
+        if (str.length() == 0) {
+            System.out.println(permutation);
+            return;
+        }
+        for (int i = 0; i < str.length(); i++) {
+            char currChar = str.charAt(i);
+            //"abc" -> "ab"
+            String newStr = str.substring(0, i) + str.substring(i + 1);
+            printPerm(newStr, permutation + currChar);
+        }
+    }
+    public static void main(String args[]){
+        String str="abc";
+        printPerm(str, "");
+    }
+}
diff --git a/src/binod/UniqueSubSequences.java b/src/binod/UniqueSubSequences.java
@@ -0,0 +1,25 @@
+package binod;
+import java.util.HashSet;
+public class UniqueSubSequences {
+    public static void subsequences(String str, int idx, String newString, HashSet<String> set) {
+        if (idx == str.length()) {
+            if (set.contains(newString)) {
+                return;
+            } else {
+                System.out.println(newString);
+                set.add(newString);
+                return;
+            }
+        }
+        char currChar = str.charAt(idx);
+        //to be
+        subsequences(str, idx + 1, newString + currChar, set);
+        //or  not to be
+        subsequences(str, idx + 1, newString, set);
+    }
+    public static void main(String[] args) {
+        String str = "aaa";
+        HashSet<String> set = new HashSet<>();
+        subsequences(str, 0, "", set);
+    }
+}
