a simple intersection

c/intersection.c

@@ -0,0 +1,68 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define MAX_DATA 50
+
+typedef struct ArrayList {
+    int cap;
+    int index;
+    int data[];
+} ArrayList;
+
+ArrayList *new_array_list(int cap) {
+    ArrayList *arr = malloc(sizeof(ArrayList) + cap * sizeof(int));
+
+    if (arr == NULL) {
+        fprintf(stderr, "ERROR: cannot allocate mem for arraylist\n");
+    }
+    arr->cap = cap;
+    arr->index = 0;
+
+    return (arr);
+}
+
+void push(ArrayList *arr, int val) {
+    if (arr->index == arr->cap) {
+        fprintf(stderr, "ERROR: cannot append to array at capacity");
+        exit(1);
+    }
+
+    arr->data[arr->index] = val;
+    arr->index++;
+}
+
+void pop(ArrayList *arr) {
+    if (arr->index == 0) {
+        fprintf(stderr, "ERROR: canoot pop from empty array");
+        exit(1);
+    }
+
+    arr->index--;
+}
+
+/* for now we only return the indices on the left that that are in the right */
+ArrayList *intersection(int left[], int right[], int left_len, int right_len) {
+    ArrayList *arr = new_array_list(left_len);
+
+    for (int i = 0; i < left_len; i++) {
+        for (int j = 0; j < right_len; j++) {
+            if (left[i] == right[j]) {
+                push(arr, left[i]);
+            }
+        }
+    }
+
+    return (arr);
+}
+
+int main() {
+    int a[5] = {1, 2, 3, 4, 8};
+    int b[5] = {4, 5, 6, 7, 8};
+
+    ArrayList *arr = intersection(a, b, 5, 5);
+    for (int i = 0; i < 2; i++) {
+        printf("%d ", arr->data[i]);
+    }
+    printf("\n");
+    return (0);
+}