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Lexicographic Order
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package com.hrishikeshmishra.practices.string; | |
import java.util.Arrays; | |
import static com.hrishikeshmishra.practices.string.LexicographicOrder.getNextPermutation; | |
/** | |
* Problem: | |
* Lexicographic Order | |
* Generates permutations using lexicographic ordering. | |
* ; | |
* ; | |
* Algorithm: | |
* - Start from end and find next smaller value between two adjacent | |
* - Swap that value with next large number from end | |
* - And sort all number from accesending order | |
* ; | |
* ; | |
* | |
* @author hrishikesh.mishra | |
* @quora https://www.quora.com/How-would-you-explain-an-algorithm-that-generates-permutations-using-lexicographic-ordering | |
* @link http://hrishikeshmishra.com/lexicographic-order/ | |
*/ | |
public class LexicographicOrder { | |
public static int[] getNextPermutation(int[] array) { | |
int x = array.length - 1; | |
/** Checking for possibility **/ | |
while (x > 0 && array[x - 1] >= array[x]) { | |
x--; | |
} | |
/** When all permutation done **/ | |
if (x <= 0) { | |
throw new RuntimeException("This was last permutation."); | |
} | |
int y = array.length - 1; | |
/** Find next largest fox array[x - 1] **/ | |
while (array[y] <= array[x - 1]) { | |
y--; | |
} | |
/** Swap **/ | |
swap(array, x - 1, y); | |
reverse(array, x, array.length - 1); | |
return array; | |
} | |
private static void reverse(int[] array, int left, int right) { | |
while (left < right) { | |
swap(array, left, right); | |
left++; | |
right--; | |
} | |
} | |
private static void swap(int[] array, int x, int y) { | |
int temp = array[x]; | |
array[x] = array[y]; | |
array[y] = temp; | |
} | |
} | |
class LexicographicOrderTest { | |
public static void main(String[] args) { | |
int[] array = {5, 1, 7, 6, 3, 9, 8, 4, 2}; | |
System.out.println("Array : " + Arrays.toString(array)); | |
System.out.println("Next permutations : " + Arrays.toString(getNextPermutation(array))); | |
} | |
} |
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