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diff --git a/count_num_complete_component.c b/count_num_complete_component.c
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+// 2685. Count the Number of Complete Components
+#include "leetcode.h"
+
+/*
+ * you are given an integer 'n'. there is an undirected graph with 'n' vertices,
+ * numbered from 0 to 'n - 1'. you are given a 2d integer array 'edges' where
+ * 'edges[i] = [a_i, b_i]' denotes that there exists an undirected edge
+ * connecting vertices 'a_i' and 'b_i'. return the number of complete connected
+ * components of the graph. a connected component is a subgraph of a graph in
+ * which there exists a path between any two vertices and no vertex of the
+ * subgraph shares an edge with a vertex outside of the subgraph. a connected
+ * component is said to be complete if there exists an edge between every pair
+ * of its vertices
+ */
+
+int countCompleteComponents(int n, int **edges, int edgesSize,
+ int *edgesColSize) {
+ int *vertices = (int *)calloc(n, sizeof(int));
+ int *edge_cnt = (int *)calloc(n, sizeof(int));
+ int *vert_cnt = (int *)calloc(n, sizeof(int));
+ int group = 1, ans = 0;
+ for (int i = 0; i < edgesSize; i++) {
+ int v1 = edges[i][0];
+ int v2 = edges[i][1];
+ if (!(vertices[v1] + vertices[v2])) {
+ vertices[v1] = vertices[v2] = group;
+ edge_cnt[group] = 2;
+ vert_cnt[group++] = 1;
+ } else if (!vertices[v1]) {
+ vertices[v1] = vertices[v2];
+ ++edge_cnt[vertices[v2]];
+ ++vert_cnt[vertices[v2]];
+ } else if (!vertices[v2]) {
+ vertices[v2] = vertices[v1];
+ ++edge_cnt[vertices[v1]];
+ ++vert_cnt[vertices[v1]];
+ } else if (vertices[v1] == vertices[v2])
+ ++vert_cnt[vertices[v1]];
+ else {
+ vert_cnt[vertices[v1]] += vert_cnt[vertices[v2]] + 1;
+ edge_cnt[vertices[v1]] += edge_cnt[vertices[v2]];
+ edge_cnt[vertices[v2]] = vert_cnt[vertices[v2]] = 0;
+ for (int i = 0; i < n; i++)
+ if (vertices[i] == vertices[v2])
+ vertices[i] = vertices[v1];
+ }
+ }
+ int connect_cnt = 0;
+ for (int i = 1; i < group; i++) {
+ int edges = edge_cnt[i], verts = vert_cnt[i];
+ if (edges && (edges * (edges - 1) / 2 == verts))
+ ++ans;
+ connect_cnt += edges;
+ }
+ free(vert_cnt);
+ free(edge_cnt);
+ free(vertices);
+ return ans + (n - connect_cnt);
+}
+
+int main() {
+ int e1i[4][2] = {{0, 1}, {0, 2}, {1, 2}, {3, 4}},
+ e2i[5][2] = {{0, 1}, {0, 2}, {1, 2}, {3, 4}, {3, 5}};
+ struct two_d_arr e1, e2;
+ two_d_arr_init(&e1, ARRAY_SIZE(e1i), ARRAY_SIZE(e1i[0]), e1i);
+ two_d_arr_init(&e2, ARRAY_SIZE(e2i), ARRAY_SIZE(e2i[0]), e2i);
+ printf("%d\n", countCompleteComponents(6, e1.arr, e1.row_size,
+ e1.col_size)); // expect: 3
+ printf("%d\n", countCompleteComponents(6, e2.arr, e2.row_size,
+ e2.col_size)); // expect: 1
+ two_d_arr_free(&e1);
+ two_d_arr_free(&e2);
+}