init chapter3

Author: Heatwave

chapter-3-control-flow/1.binsearch.c

@@ -0,0 +1,92 @@
+#include <stdio.h>
+#include <time.h>
+
+
+#define ARRAY_LEN 500000
+
+int binsearch(int, int[], int);
+int binsearchFast(int, int[], int);
+
+main()
+{
+	clock_t start, finish;
+	int i, v[ARRAY_LEN];
+	for (i = 0; i < ARRAY_LEN; i++)
+		v[i] = i;
+
+	start = clock();
+	int p;
+	for (i = 0; i < ARRAY_LEN; i++) {
+		p = binsearch(i, v, ARRAY_LEN);
+		//printf("%d at %d\n", i, p);
+	}
+	finish = clock();
+
+	printf("binsearch duration: %f\n", ((double)(finish - start)) / CLOCKS_PER_SEC);
+
+	//printf("binsearchFast:\n");
+
+	start = clock();
+	for (i = 0; i < ARRAY_LEN; i++) {
+		p = binsearchFast(i, v, ARRAY_LEN);
+		//printf("%d at %d\n", i, p);
+	}
+	finish = clock();
+	printf("binsearchFast duration: %f\n", ((double)(finish - start)) / CLOCKS_PER_SEC);
+
+	for (i = -10000; i < ARRAY_LEN; i++) {
+		p = binsearchFast(i, v, ARRAY_LEN);
+		if (i < 0 && p != -1)
+			break;
+		else if (i >= 0 && p != i)
+			break;
+	}
+	printf("i: %d\n", i);
+}
+
+/* binsearch: find x in v[0] <= v[1] <= ... v[n-1] */
+int binsearch(int x, int v[], int n)
+{
+	int low, high, mid;
+
+	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 binsearchFast(int x, int v[], int n)
+{
+	int low, high, mid;
+
+	low = 0;
+	high = n - 1;
+	while (low <= high) {
+		mid = (low + high) / 2;
+
+		if (x <= v[mid])
+			high = mid - 1;
+		else
+			low = mid + 1;
+	}
+
+	if (x == v[mid])
+		return mid;
+	else if (x > v[mid])
+		mid += 1;
+	else
+		mid -= 1;
+
+	if (mid < 0 || mid > n - 1)
+		return -1;
+	else
+		return mid;
+}