exercise 3.01

chapter_3/exercise_3_01.c

@@ -0,0 +1,87 @@
+#include <bits/time.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/time.h>
+#include <time.h>
+
+/* binsearch: find x in v[0] <= v[1] <= ... <= v[n - 1] */
+int binsearch(int x, int v[], int n);
+int binsearch2(int x, int v[], int n);
+void genrandseq(int v[], int n);
+void test(char fname[], int (*f)(int x, int v[], int n), int v[], int n);
+
+int main()
+{
+    const int n = (int)1e4;
+    int *v = malloc(sizeof(int) * n);
+
+    test("binsearch", binsearch, v, n);
+    test("binsearch2", binsearch2, v, n);
+
+    return 0;
+}
+
+int binsearch(int x, int v[], int n)
+{
+    int mid = 0;
+    int low = 0, high = n - 1;
+    while (low <= high) {
+        mid = (low + high) / 2;
+        if (x < v[mid]) {
+            high = mid - 1;
+        } else if (x > v[mid]) {
+            low = mid + 1;
+        } else {
+            return mid;
+        }
+    }
+
+    return -1;
+}
+
+int binsearch2(int x, int v[], int n)
+{
+    int mid = 0;
+    int low = 0, high = n - 1;
+    while (low < high) {
+        mid = (low + high) / 2;
+
+        if (x <= v[mid]) {
+            high = mid;
+        } else {
+            low = mid + 1;
+        }
+    }
+
+    if (v[low] == x) return low;
+    return -1;
+}
+
+void genrandseq(int v[], int n)
+{
+    srand(time(NULL));
+    for (int i = 0; i < n; ++i) {
+        int base = 0;
+        if (i > 0) base = v[i - 1];
+        v[i] = base + rand() / (RAND_MAX / 3);
+    }
+}
+
+void test(char fname[], int (*f)(int x, int v[], int n), int v[], int n)
+{
+    const int run = (int)1e4;
+    struct timespec start, stop;
+    int tsum = 0;
+
+    for (int i = 0; i < run; ++i) {
+        genrandseq(v, n);
+        int target = v[rand() % n];
+        clock_gettime(CLOCK_MONOTONIC_RAW, &start);
+        f(target, v, n);
+        clock_gettime(CLOCK_MONOTONIC_RAW, &stop);
+        int elapse = (stop.tv_sec - start.tv_sec) * 1e6 + (stop.tv_nsec - start.tv_nsec) / 1e3;
+        tsum += elapse;
+    }
+
+    printf("`%s` used %d ms\n", fname, tsum);
+}