translation: Add Python and Java code for EN version (#1345)

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* Add Python and Java code for EN version

en/codes/java/chapter_computational_complexity/recursion.java

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+/**
+ * File: recursion.java
+ * Created Time: 2023-08-24
+ * Author: krahets (krahets@163.com)
+ */
+
+package chapter_computational_complexity;
+
+import java.util.Stack;
+
+public class recursion {
+    /* Recursion */
+    static int recur(int n) {
+        // Termination condition
+        if (n == 1)
+            return 1;
+        // Recursive: recursive call
+        int res = recur(n - 1);
+        // Return: return result
+        return n + res;
+    }
+
+    /* Simulate recursion with iteration */
+    static int forLoopRecur(int n) {
+        // Use an explicit stack to simulate the system call stack
+        Stack<Integer> stack = new Stack<>();
+        int res = 0;
+        // Recursive: recursive call
+        for (int i = n; i > 0; i--) {
+            // Simulate "recursive" by "pushing onto the stack"
+            stack.push(i);
+        }
+        // Return: return result
+        while (!stack.isEmpty()) {
+            // Simulate "return" by "popping from the stack"
+            res += stack.pop();
+        }
+        // res = 1+2+3+...+n
+        return res;
+    }
+
+    /* Tail recursion */
+    static int tailRecur(int n, int res) {
+        // Termination condition
+        if (n == 0)
+            return res;
+        // Tail recursive call
+        return tailRecur(n - 1, res + n);
+    }
+
+    /* Fibonacci sequence: Recursion */
+    static int fib(int n) {
+        // Termination condition f(1) = 0, f(2) = 1
+        if (n == 1 || n == 2)
+            return n - 1;
+        // Recursive call f(n) = f(n-1) + f(n-2)
+        int res = fib(n - 1) + fib(n - 2);
+        // Return result f(n)
+        return res;
+    }
+
+    /* Driver Code */
+    public static void main(String[] args) {
+        int n = 5;
+        int res;
+
+        res = recur(n);
+        System.out.println("\nSum result of the recursive function res = " + res);
+
+        res = forLoopRecur(n);
+        System.out.println("\nSum result using iteration to simulate recursion res = " + res);
+
+        res = tailRecur(n, 0);
+        System.out.println("\nSum result of the tail-recursive function res = " + res);
+
+        res = fib(n);
+        System.out.println("\nThe " + n + "th number in the Fibonacci sequence is " + res);
+    }
+}