# Java Program to Compute Combinations using Recurrence Relation for nCr

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This is a java program to generate and print all possible combinations out of a, b, c, d, e. The trick here is to start with one letter combinations, then with two letter combinations and so on.

Here is the source code of the Java Program to Generate All Possible Combinations Out of a, b, c, d, e. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

1. `//This is a java program to print all possible combinations out of a, b, c, d, e`
2. ` `
3. `public class All_Possible_Combinatons `
4. `{`
5. `    static void printCombinations(char[] sequence, int N) `
6. `    {`
7. `        char[] data = new char[N];`
8. `        for (int r = 0; r < sequence.length; r++)`
9. `            combinations(sequence, data, 0, N - 1, 0, r);`
10. `    }`
11. ` `
12. `    static void combinations(char[] sequence, char[] data, int start, int end,`
13. `            int index, int r) `
14. `    {`
15. ` `
16. `        if (index == r) `
17. `        {`
18. `            for (int j = 0; j < r; j++)`
19. `                System.out.print(data[j] + " ");`
20. `            System.out.println();`
21. `        }`
22. ` `
23. `        for (int i = start; i <= end && ((end - i + 1) >= (r - index)); i++) `
24. `        {`
25. `            data[index] = sequence[i];`
26. `            combinations(sequence, data, i + 1, end, index + 1, r);`
27. `        }`
28. `    }`
29. ` `
30. `    public static void main(String args[]) `
31. `    {`
32. `        char[] sequence = { 'a', 'b', 'c', 'd', 'e' };`
33. `        System.out.print("The combinations are: ");`
34. `        printCombinations(sequence, sequence.length);`
35. `    }`
36. `}`

Output:

```\$ javac All_Possible_Combinatons.java
\$ java All_Possible_Combinatons

The combinations are:
a
b
c
d
e
a b
a c
a d
a e
b c
b d
b e
c d
c e
d e
a b c
a b d
a b e
a c d
a c e
a d e
b c d
b c e
b d e
c d e
a b c d
a b c e
a b d e
a c d e
b c d e```

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