-
Notifications
You must be signed in to change notification settings - Fork 0
/
PermutationCombination.java
99 lines (87 loc) · 3.18 KB
/
PermutationCombination.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
package com.algos.string;
import java.util.Stack;
/**
* Comment here about the class
* User: Fizal
* Date: 7/11/2016
* Time: 9:46 PM
*/
public class PermutationCombination {
public static void main(String[] args) {
// String alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
String word = "charm";
System.out.println(" ----------- Permutations -------------");
permutation(word);
System.out.println(" ----------- Combinations -------------");
combination(word);
System.out.println(" ----------- Combinations 2 -------------");
combination2(word);
}
/**
* print n! permutation of the characters of the string s (in order)
*/
public static void permutation(String s) {
permutation("", s);
}
private static int count = 0;
private static void permutation(String prefix, String s) {
if (s.isEmpty()) {
System.out.println(++count + ": " + prefix);
} else {
for (int i = 0; i < s.length(); i++) {
final String newPrefix = prefix + s.charAt(i);
final String newString = s.substring(0, i) + s.substring(i + 1, s.length());
permutation(newPrefix, newString);
}
}
}
/**
* Prints (2^n)-1 combinations of a given string, where n is the length of the string
* @param str
*/
private static void combination(String str) {
count = 0;
Stack<Character> result = new Stack<>();
for (int i = 1; i <= str.length(); ++i) {
combination(str, 0, i, result);
}
}
private static void combination(String str, int index, int number, Stack<Character> result) {
if (number == 0) {
System.out.println(++count + ": " + result);
return;
}
if (index == str.length()) {
return;
}
// select the character str[index]
result.push(str.charAt(index));
combination(str, index + 1, number - 1, result);
result.pop();
// ignore the character str[index]
combination(str, index + 1, number, result);
}
/**
* Combination generation using bit-wise operation. If the input string is 2 characters in length,
* then 3 (2^2 -1) combinations like 01, 10, 11 are possible.
*
* For each combination, print the character at the index where bit is set.
* @param str
*/
public static void combination2(String str) {
count = 0;
int numberOfBits = str.length();
int totalCombinations = (int)Math.pow(2, numberOfBits) -1; // 2^n -1
for (int i = 1; i <= totalCombinations; i++) {
//convert integer to binary, e.g., 2 = 0010. # of bits depends is equal to the size of the input string
final String binary = String.format("%"+ str.length() +"s", Integer.toBinaryString(i)).replace(' ', '0');
System.out.print(++count + ": ");
for (int j = 0; j < binary.length(); j++) {
if(binary.charAt(j)=='1'){
System.out.print(str.charAt(j));
}
}
System.out.println();
}
}
}