Data commit

Task/Quickselect-algorithm/C/quickselect-algorithm.c

@@ -0,0 +1,35 @@
+#include <stdio.h>
+#include <string.h>
+
+int qselect(int *v, int len, int k)
+{
+#	define SWAP(a, b) { tmp = v[a]; v[a] = v[b]; v[b] = tmp; }
+	int i, st, tmp;
+
+	for (st = i = 0; i < len - 1; i++) {
+		if (v[i] > v[len-1]) continue;
+		SWAP(i, st);
+		st++;
+	}
+
+	SWAP(len-1, st);
+
+	return k == st	?v[st]
+			:st > k	? qselect(v, st, k)
+				: qselect(v + st, len - st, k - st);
+}
+
+int main(void)
+{
+#	define N (sizeof(x)/sizeof(x[0]))
+	int x[] = {9, 8, 7, 6, 5, 0, 1, 2, 3, 4};
+	int y[N];
+
+	int i;
+	for (i = 0; i < 10; i++) {
+		memcpy(y, x, sizeof(x)); // qselect modifies array
+		printf("%d: %d\n", i, qselect(y, 10, i));
+	}
+
+	return 0;
+}