dynamicXcoder
diff --git a/‎lectures/14-recursion/Recursion - Permutations.pdf
380 KB b/‎lectures/14-recursion/Recursion - Permutations.pdf
380 KB
diff --git a/‎lectures/14-recursion/code/src/com/kunal/strings/Permutations.java
Lines changed: 61 additions & 0 deletions b/‎lectures/14-recursion/code/src/com/kunal/strings/Permutations.java
Lines changed: 61 additions & 0 deletions
@@ -0,0 +1,61 @@
+package com.kunal.strings;
+
+import java.util.ArrayList;
+
+public class Permutations {
+    public static void main(String[] args) {
+//        permutations("", "abc");
+
+//        ArrayList<String> ans = permutationsList("", "abc");
+//        System.out.println(ans);
+
+        System.out.println(permutationsCount("", "abcd"));
+    }
+
+    static void permutations(String p, String up) {
+        if (up.isEmpty()) {
+            System.out.println(p);
+            return;
+        }
+        char ch = up.charAt(0);
+        for (int i = 0; i <= p.length(); i++) {
+            String f = p.substring(0, i);
+            String s = p.substring(i, p.length());
+            permutations(f + ch + s, up.substring(1));
+        }
+    }
+
+    static ArrayList<String> permutationsList(String p, String up) {
+        if (up.isEmpty()) {
+            ArrayList<String> list = new ArrayList<>();
+            list.add(p);
+            return list;
+        }
+        char ch = up.charAt(0);
+
+        // local to this call
+        ArrayList<String> ans = new ArrayList<>();
+
+        for (int i = 0; i <= p.length(); i++) {
+            String f = p.substring(0, i);
+            String s = p.substring(i, p.length());
+            ans.addAll(permutationsList(f + ch + s, up.substring(1)));
+        }
+        return ans;
+    }
+
+    static int permutationsCount(String p, String up) {
+        if (up.isEmpty()) {
+            return 1;
+        }
+        int count = 0;
+        char ch = up.charAt(0);
+        for (int i = 0; i <= p.length(); i++) {
+            String f = p.substring(0, i);
+            String s = p.substring(i, p.length());
+            count = count + permutationsCount(f + ch + s, up.substring(1));
+        }
+        return count;
+    }
+
+}