mirror of https://github.com/TheAlgorithms/C
90 lines
1.9 KiB
C
90 lines
1.9 KiB
C
/**
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* @file union_find.c
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* @brief [Union
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* find](https://en.wikipedia.org/wiki/Disjoint-set_data_structure) algorithm.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#define MAX_SIZE 1000 /**< maximum number of elements in the set */
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/**
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* @brief Find index of or value in an array
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*
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* @param [in,out] p array to search and update
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* @param x value to search
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* @return value at the index `x`
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*/
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int find(int *p, int x)
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{
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if (x >= MAX_SIZE)
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{
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fprintf(stderr, "Out-of bounds value\n");
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exit(EXIT_FAILURE);
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}
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if (p[x] == x)
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{
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return x;
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}
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else
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{
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p[x] = find(p, p[x]);
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return p[x];
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}
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}
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/**
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* @brief Function to join
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* @param [in,out] p array to join in
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* @param x value or index to join to
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* @param y value or index to join from
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*/
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void join(int *p, int x, int y) { p[find(p, x)] = find(p, y); }
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/** Main function */
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int main()
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{
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int union_set[MAX_SIZE];
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// Have all array indexes that you need to use reference themselves
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for (int i = 0; i < 10; i++)
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{
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union_set[i] = i;
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}
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// p = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
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join(union_set, 3, 5);
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printf("The array is now: ");
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for (int i = 0; i < 10; i++)
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{
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printf("%d ", union_set[i]);
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}
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printf("\n");
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// Now 3 and 5 are groupped together, that is find(3) = find(5)
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// p = {0, 1, 2, 5, 4, 5, 6, 7, 8, 9}
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join(union_set, 3, 8);
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printf("The array is now: ");
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for (int i = 0; i < 10; i++)
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{
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printf("%d ", union_set[i]);
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}
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printf("\n");
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// Now 3, 5 and are groupped together, find(3) = find(5) = find(8)
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// p = {0, 1, 2, 5, 4, 8, 6, 7, 8, 9}
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join(union_set, 0, 5);
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if (find(union_set, 0) == find(union_set, 3))
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{
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printf("0 and 3 are groupped together\n");
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}
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printf("The array is now: ");
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for (int i = 0; i < 10; i++)
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{
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printf("%d ", union_set[i]);
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}
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printf("\n");
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return 0;
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}
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