diff --git a/inc/hnsw.h b/inc/hnsw.h
index 400adb4..be8a110 100644
--- a/inc/hnsw.h
+++ b/inc/hnsw.h
@@ -3,40 +3,27 @@
 #include <stdio.h>
 #include "utils.h"
 
-typedef struct NSWGraph
-{
-
-} NSWGraph;
+// you can add more structures here or modify existing structrues.
 
 typedef struct HNSWGraph
 {
     size_t layers_num; // number of layers
-    NSWGraph **layers;
 } HNSWGraph;
 
 typedef struct HNSWContext
 {
     size_t dim;       // dimension of dataset
     size_t len;       // size of dataset
+    VecData *data;    // vectors will be loaded into this array
     HNSWGraph *graph; // graph of HNSW
 } HNSWContext;
 
+// you can define some help functions here
 
-typedef struct {
-    unsigned int* visited;
-    unsigned int size;
-    unsigned int mark;
-} VisitedList;
-
-// help functions
 
 // public functions
-HNSWContext *init_hnsw_context(const char *file_path, size_t dim, size_t len);
-void insert_vec(HNSWContext *ctx, VecData vec);
-void approximate_knn(HNSWContext *ctx, VecData *results);
-
-VisitedList* visited_list_new(int size);
-void visited_list_reset(VisitedList* vl);
-unsigned int visited_list_get_visit_mark(VisitedList* vl);
-unsigned int* visited_list_get_visited(VisitedList* vl);
-void visited_list_free(VisitedList* vl);
+// Please do not modify these function signatures!
+// To simply our program, we do not consider reclaiming memory space here.
+// Please implement these functions according to HNSW algorithm.
+HNSWContext *hnsw_init_context(const char *filename, size_t dim, size_t len);
+void hnsw_approximate_knn(HNSWContext *ctx, VecData *q, int *results, int k);
diff --git a/inc/utils.h b/inc/utils.h
index 4adc2c2..02e9bcf 100644
--- a/inc/utils.h
+++ b/inc/utils.h
@@ -1,8 +1,22 @@
+#pragma once
+
+#include <stdio.h>
+
+#define GLOBAL_DIM 128
 
 typedef struct {
     int id;
-    float* vector;
+    float* vec;
 } VecData;
 
+typedef struct {
+    FILE* stream;
+    char *filename;
+    int offset;
+} FileContext;
+
 float vec_dist(VecData x, VecData y);
-VecData* fvecs_read(const char* filename, int* bounds, int* num);
\ No newline at end of file
+FileContext* init_file_context(const char *filename);
+void read_4bytes(FileContext* ctx, void* dst);
+void read_vec_data(FileContext* ctx, void* dst);
+void free_file_context(FileContext* ctx);
diff --git a/src/hnsw.c b/src/hnsw.c
index 98d3995..7bf643d 100644
--- a/src/hnsw.c
+++ b/src/hnsw.c
@@ -1,30 +1,54 @@
+#include <limits.h>
 #include "hnsw.h"
 
+HNSWContext *hnsw_init_context(const char *filename, size_t dim, size_t len)
+{
+    HNSWContext *ctx = (HNSWContext *) malloc(sizeof(HNSWContext));
+    ctx->dim = dim;
+    ctx->len = len;
+    ctx->data = (VecData *) malloc(sizeof(VecData) * len);
 
-VisitedList* visited_list_new(int size) {
-    VisitedList* vl = malloc(sizeof(VisitedList));
-    vl->size = size;
-    vl->mark = 1;
-    vl->visited = calloc(size, sizeof(unsigned int));
-    return vl;
-}
+    // init file context
+    FileContext* f_ctx = init_file_context(filename);
 
-void visited_list_reset(VisitedList* vl) {
-    if (++vl->mark == 0) {
-        vl->mark = 1;
-        memset(vl->visited, 0, sizeof(unsigned int) * vl->size);
+    for (int i = 0; i < len; i++)
+    {
+        ctx->data[i].id = i;
+        ctx->data[i].vec = (float *) malloc(sizeof(float) * GLOBAL_DIM);
+        read_vec_data(f_ctx, ctx->data[i].vec);
     }
-}
 
-unsigned int visited_list_get_visit_mark(VisitedList* vl) {
-    return vl->mark;
+    free_file_context(f_ctx);
+    return ctx;
 }
 
-unsigned int* visited_list_get_visited(VisitedList* vl) {
-    return vl->visited;
-}
+void hnsw_approximate_knn(HNSWContext *ctx, VecData *q, int *results, int k)
+{
+    // sort existing vectors
+    for (size_t i = 0; i < k && i < ctx->len - 1; i++)
+    {
+        float min_dist = vec_dist(*q, ctx->data[i]);
+        size_t idx = i;
+        for (size_t j = i + 1; j < ctx->len; j++)
+        {
+            float dist = vec_dist(*q, ctx->data[j]);
+            if (dist < min_dist)
+            {
+                min_dist = dist;
+                idx = i;
+            }
+        }
+        if (idx != i)
+        {
+            VecData tmp = ctx->data[idx];
+            ctx->data[idx] = ctx->data[i];
+            ctx->data[i] = tmp;
+        }
+    }
 
-void visited_list_free(VisitedList* vl) {
-    free(vl->visited);
-    free(vl);
-}
\ No newline at end of file
+    // copy results
+    for (int i = 0; i < k; i++)
+    {
+        results[i] = ctx->data[i].id;
+    }
+}
diff --git a/src/test.c b/src/test.c
index 46a1ae5..5aa49fd 100644
--- a/src/test.c
+++ b/src/test.c
@@ -1,21 +1,23 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include "hnsw.h"
 #include "utils.h"
 
 
-int main() {
+int main(int argc, char *argv[]) {
     
-    int num = 0;
-    VecData* vecs = fvecs_read("../dataset/siftsmall_base.fvecs", NULL, &num);
-    printf("num: %d\n", num);
-    printf("id of vector 1: %d\n", vecs[0].id);
-    printf("test distance: %f\n", vec_dist(vecs[0], vecs[1]));
-
-    // Free memory
-    for (int i = 0; i < num; i++) {
-        free(vecs[i].vector);
+    FileContext* f_ctx = init_file_context(argv[1]);
+    VecData data;
+    data.vec = malloc(sizeof(float) * GLOBAL_DIM);
+    for (int i = 0; i < 100; i++)
+    {
+        read_vec_data(f_ctx, data.vec);
+        for (int j = 0; j < GLOBAL_DIM; j++) 
+        {
+            printf("%f ", data.vec[j]);
+        }
+        putchar('\n');
     }
-    free(vecs);
     return 0;
 }
 
diff --git a/src/utils.c b/src/utils.c
index 40cf79b..50402fc 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -1,73 +1,52 @@
 #include "utils.h"
-#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>
 
-float vec_dist(VecData x, VecData y) {
+float vec_dist(VecData x, VecData y)
+{
     float sum = 0.0;
-    for (int i = 0; i < 128; i++) {
-        float diff = x.vector[i] - y.vector[i];
+    for (size_t i = 0; i < GLOBAL_DIM; i++)
+    {
+        float diff = x.vec[i] - y.vec[i];
         sum += diff * diff;
     }
-    return sqrt(sum);
+    return sum;
 }
 
-VecData* fvecs_read(const char* filename, int* bounds, int* num) {
-    FILE* fid = fopen(filename, "rb");
-    if (fid == NULL) {
+FileContext *init_file_context(const char *filename)
+{
+    FileContext *ctx = (FileContext *)malloc(sizeof(FileContext));
+    ctx->filename = (char *)malloc(strlen(filename) + 1L);
+    memcpy(ctx->filename, filename, strlen(filename) + 1L);
+
+    ctx->stream = fopen(filename, "rb");
+    if (ctx->stream == NULL)
+    {
         fprintf(stderr, "I/O error : Unable to open the file %s\n", filename);
         exit(EXIT_FAILURE);
     }
+    ctx->offset = 0;
+    return ctx;
+}
 
-    int d; 
-    fread(&d, sizeof(int), 1, fid);
-
-
-    fseek(fid, 0, SEEK_END);
-    long file_size = ftell(fid);
-    fseek(fid, 0, SEEK_SET);
-    long vec_size = (long) d * sizeof(float);
-    long vec_count = (file_size - sizeof(int)) / vec_size;
-
-    int a = 1;
-    int bmax = vec_count;
-    int b = bmax;
-
-    if (bounds != NULL) {
-        if (bounds[1] == 1) {
-            b = bounds[0];
-        } else if (bounds[1] == 2) {
-            a = bounds[0];
-            b = bounds[1];
-        }
-    }
-
-    if (a < 1 || b > bmax || b < a) {
-        VecData* v = NULL;
-        fclose(fid);
-        return v;
-    }
-
-    int n = b - a + 1;
-    fseek(fid, (a - 1) * vec_size, SEEK_SET);
-
-    
-    // Read n vectors
-    VecData* v = malloc(n * sizeof(VecData));
-    for (int i = 0; i < n; i++) {
-        VecData vec;
-        vec.id = i + a;
-        vec.vector = malloc(d * sizeof(float));
-        fread(vec.vector, sizeof(float), d, fid);
-        v[i] = vec;
-    }
+void read_4bytes(FileContext *ctx, void *dst)
+{
+    size_t s = fread(dst, 4L, 1, ctx->stream);
+    assert(s == 1L);
+}
 
+void read_vec_data(FileContext *ctx, void *dst)
+{
+    read_4bytes(ctx, dst);
+    size_t s = fread(dst, 4L, GLOBAL_DIM, ctx->stream);
+    assert(s == GLOBAL_DIM);
+}
 
-    fclose(fid);
-    if (num != NULL) {
-        *num = n;
-    }
-    return v;
-}
\ No newline at end of file
+void free_file_context(FileContext* ctx)
+{
+    fclose(ctx->stream);
+    free(ctx->filename);
+    free(ctx);
+}