union_find.c File Reference

Union find algorithm. More...

#include <stdio.h>
#include <stdlib.h>

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Macros
#define	MAX_SIZE   1000
	maximum number of elements in the set

Functions
int	find (int *p, int x)
	Find index of or value in an array. More...
void	join (int *p, int x, int y)
	Function to join. More...
int	main ()
	Main function. More...

Detailed Description

Union find algorithm.

Function Documentation

find()

int find	(	int *	p,
		int	x
	)

Find index of or value in an array.

Parameters

[in,out]	p	array to search and update
	x	value to search

Returns

value at the index x

{
    if (x >= MAX_SIZE)
    {
        fprintf(stderr, "Out-of bounds value\n");
        exit(EXIT_FAILURE);
    }
 
    if (p[x] == x)
    {
        return x;
    }
    else
    {
        p[x] = find(p, p[x]);
        return p[x];
    }
}

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join()

void join	(	int *	p,
		int	x,
		int	y
	)

Function to join.

Parameters

[in,out]	p	array to join in
	x	value or index to join to
	y	value or index to join from

{ p[find(p, x)] = find(p, y); }

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main()

int main

(

void

)

Main function.

{
    int union_set[MAX_SIZE];
 
    // Have all array indexes that you need to use reference themselves
    for (int i = 0; i < 10; i++)
    {
        union_set[i] = i;
    }
    // p = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
 
    join(union_set, 3, 5);
    printf("The array is now: ");
    for (int i = 0; i < 10; i++)
    {
        printf("%d ", union_set[i]);
    }
    printf("\n");
    // Now 3 and 5 are groupped together, that is find(3) = find(5)
    // p = {0, 1, 2, 5, 4, 5, 6, 7, 8, 9}
 
    join(union_set, 3, 8);
    printf("The array is now: ");
    for (int i = 0; i < 10; i++)
    {
        printf("%d ", union_set[i]);
    }
    printf("\n");
 
    // Now 3, 5 and are groupped together, find(3) = find(5) = find(8)
    // p = {0, 1, 2, 5, 4, 8, 6, 7, 8, 9}
    join(union_set, 0, 5);
    if (find(union_set, 0) == find(union_set, 3))
    {
        printf("0 and 3 are groupped together\n");
    }
    printf("The array is now: ");
    for (int i = 0; i < 10; i++)
    {
        printf("%d ", union_set[i]);
    }
    printf("\n");
 
    return 0;
}

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