fix lgtm error and add basic docs

Author: kvedala

misc/union_find.c

@@ -1,46 +1,89 @@
+/**
+ * @file union_find.c
+ * @brief [Union
+ * find](https://en.wikipedia.org/wiki/Disjoint-set_data_structure) algorithm.
+ */
 #include <stdio.h>
+#include <stdlib.h>
+#define MAX_SIZE 1000 /**< maximum number of elements in the set */
 
-int p[1000000];
-int find(int x)
+/**
+ * @brief Find index of or value in an array
+ *
+ * @param [in,out] p array to search and update
+ * @param x value to search
+ * @return value at the index `x`
+ */
+int find(int *p, int 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[x]);
+        p[x] = find(p, p[x]);
         return p[x];
     }
 }
-// Call to function join(int x, int y) to join PARAM x and y
-void join(int x, int y) { p[find(x)] = find(y); }
 
+/**
+ * @brief Function to join
+ * @param [in,out] p array to join in
+ * @param x value or index to join to
+ * @param y value or index to join from
+ */
+void join(int *p, int x, int y) { p[find(p, x)] = find(p, y); }
+
+/** Main function */
 int main()
 {
-    // Have all array indexes that you need to use refrence themselves
+    int union_set[MAX_SIZE];
+
+    // Have all array indexes that you need to use reference themselves
     for (int i = 0; i < 10; i++)
     {
-        p[i] = i;
+        union_set[i] = i;
     }
     // p = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
-    join(3, 5);
+
+    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(3, 8);
+
+    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(0, 5);
-    if (find(0) == find(3))
+    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 ", p[i]);
+        printf("%d ", union_set[i]);
     }
     printf("\n");
 
     return 0;
-}
+}