普通的选择算法（序列第k小元素）

Author: Dev-XYS

Selection.cpp

@@ -0,0 +1,57 @@
+#include <cstdio>
+
+#define ELEMENT_COUNT 10000
+
+using namespace std;
+
+int n, k, d[ELEMENT_COUNT];
+
+int partition(int l, int r)
+{
+	int x = d[r], j = l - 1;
+	for (int i = l; i <= r; i++)
+	{
+		if (d[i] <= x)
+		{
+			j++;
+			int temp = d[i];
+			d[i] = d[j];
+			d[j] = temp;
+		}
+	}
+	return j + 1;
+}
+
+int select(int k)
+{
+	int l = 0, r = n - 1;
+	while (l < r)
+	{
+		int ord = partition(l, r);
+		if (ord < k)
+		{
+			l = ord;
+		}
+		else if (ord > k)
+		{
+			r = ord - 2;
+		}
+		else
+		{
+			return d[ord - 1];
+		}
+	}
+	return d[l];
+}
+
+int main()
+{
+	scanf("%d%d", &n, &k);
+	for (int i = 0; i < n; i++)
+	{
+		scanf("%d", &d[i]);
+	}
+	int kth = select(k);
+	printf("%d", kth);
+	return 0;
+}