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Very simple java library to generate permutations, combinations and other
combinatorial sequences.
/**
* Combinatorics Library
* Copyright 2012 Dmytro Paukov [email protected]
*/
package org.paukov.combinatorics.util;
import java.math.BigDecimal;
/**
* Utility class for combinatorial package
*
* @author Dmytro Paukov
* @version 2.0
*/
public class Util {
/**
* Get minimum of three values
*/
public static int minimum(int a, int b, int c) {
int mi = a;
if (b < mi) {
mi = b;
}
if (c < mi) {
mi = c;
}
return mi;
}
/**
* Calculates factorial of the given integer value x
*
* @param x Integer value
*/
public static long factorial(long x) {
long result = 1;
for (long i = 2; i <= x; i++) {
result *= i;
}
return result;
}
/**
* Calculates factorial of the given integer value x
*
* @param x Integer value
*/
public static BigDecimal bigFactorial(long x) {
BigDecimal result = BigDecimal.valueOf(1);
for (long i = 2; i <= x; i++) {
result = result.multiply(BigDecimal.valueOf(i));
}
return result;
}
/**
* Calculates 2 in power of integer value x
*/
public static long pow2(long x) {
if (x < 0) {
return 1;
}
return 1 << x;
}
/**
* Calculates the number of k-combinations (each of size k) from a set with
* n elements (size n) (also known as the "choose function")
*
* @param n Value n
* @param k Value k
*/
public static long combination(long n, long k) {
return factorial(n) / (factorial(k) * factorial(n - k));
}
/**
* Calculates greatest common divisor (GCD) of two integer values
* a and b
*
* @param a Value a
* @param b Value b
*/
public static long gcd(long a, long b) {
if (a == 0) {
return b;
}
if (b == 0) {
return a;
}
if (a == b) {
return a;
}
if (a == 1 | b == 1) {
return 1;
}
if ((a % 2 == 0) & (b % 2 == 0)) {
return 2 * gcd(a / 2, b / 2);
}
if ((a % 2 == 0) & (b % 2 != 0)) {
return gcd(a / 2, b);
}
if ((a % 2 != 0) & (b % 2 == 0)) {
return gcd(a, b / 2);
}
return gcd(b, Math.abs(a - b));
}
/**
* Calculates lowest common multiple (LCM) of two integer values
* a and b
*
* @param a Value a
* @param b Value b
*/
public static long lcm(long a, long b) {
return (a * b) / gcd(a, b);
}
/**
* The linear interpolant is the straight line between these points
*
* @return y
*/
public static double linearInterpolation(double x0, double y0, double x1,
double y1, double x) {
return y0 + ((y1 - y0) / (x1 - x0)) * (x - x0);
}
/**
* Levenshtein distance is a measure of the similarity between two strings,
* which we will refer to as the source string source and the
* target string target. The distance is the number of
* deletions, insertions, or substitutions required to transform s into t.
*
* @param source the source string
* @param target the target string
* @return Levenshtein distance
*/
public static int levenshteinDistance(String source, String target) {
int d[][]; // matrix
int n; // length of source
int m; // length of target
int i; // iterates through source
int j; // iterates through target
char s_i; // ith character of source
char t_j; // jth character of target
int cost; // cost
// Step 1
n = source.length();
m = target.length();
if (n == 0) {
return m;
}
if (m == 0) {
return n;
}
d = new int[n + 1][m + 1];
// Step 2
for (i = 0; i <= n; i++) {
d[i][0] = i;
}
for (j = 0; j <= m; j++) {
d[0][j] = j;
}
// Step 3
for (i = 1; i <= n; i++) {
s_i = source.charAt(i - 1);
// Step 4
for (j = 1; j <= m; j++) {
t_j = target.charAt(j - 1);
// Step 5
if (s_i == t_j) {
cost = 0;
} else {
cost = 1;
}
// Step 6
d[i][j] = Util.minimum(d[i - 1][j] + 1, d[i][j - 1] + 1,
d[i - 1][j - 1] + cost);
}
}
// Step 7
return d[n][m];
}
/**
* Calculates the determinant of the matrix a
*/
public static BigDecimal detCrout(BigDecimal a[][], int n) {
for (int i = 0; i < n; i++) {
boolean nonzero = false;
for (int j = 0; j < n; j++) {
if (a[i][j].compareTo(new BigDecimal(0)) > 0) {
nonzero = true;
}
}
if (!nonzero) {
return BigDecimal.ZERO;
}
}
BigDecimal scaling[] = new BigDecimal[n];
for (int i = 0; i < n; i++) {
BigDecimal big = new BigDecimal(0);
for (int j = 0; j < n; j++) {
if (a[i][j].abs().compareTo(big) > 0) {
big = a[i][j].abs();
}
}
scaling[i] = (new BigDecimal(1)).divide(big, 100,
BigDecimal.ROUND_HALF_EVEN);
}
int sign = 1;
for (int j = 0; j < n; j++) {
for (int i = 0; i < j; i++) {
BigDecimal sum = a[i][j];
for (int k = 0; k < i; k++) {
sum = sum.subtract(a[i][k].multiply(a[k][j]));
}
a[i][j] = sum;
}
BigDecimal big = new BigDecimal(0);
int imax = -1;
for (int i = j; i < n; i++) {
BigDecimal sum = a[i][j];
for (int k = 0; k < j; k++) {
sum = sum.subtract(a[i][k].multiply(a[k][j]));
}
a[i][j] = sum;
BigDecimal cur = sum.abs();
cur = cur.multiply(scaling[i]);
if (cur.compareTo(big) >= 0) {
big = cur;
imax = i;
}
}
if (j != imax) {
for (int k = 0; k < n; k++) {
BigDecimal t = a[j][k];
a[j][k] = a[imax][k];
a[imax][k] = t;
}
BigDecimal t = scaling[imax];
scaling[imax] = scaling[j];
scaling[j] = t;
sign = -sign;
}
if (j != n - 1) {
for (int i = j + 1; i < n; i++) {
a[i][j] = a[i][j].divide(a[j][j], 100,
BigDecimal.ROUND_HALF_EVEN);
}
}
}
BigDecimal result = new BigDecimal(1);
if (sign == -1) {
result = result.negate();
}
for (int i = 0; i < n; i++) {
result = result.multiply(a[i][i]);
}
return result;
}
}