Merge pull request wangzheng0822#266 from wangjunwei87/patch-1

找到一组数据的第K大元素

Author: wangzheng0822

java/12_sorts/KthSmallest.java

@@ -0,0 +1,51 @@
+package sort;
+
+/**
+ * @author wangjunwei87
+ * @since 2019-03-10
+ */
+public class KthSmallest {
+
+ public static int kthSmallest(int[] arr, int k) {
+ if (arr == null || arr.length < k) {
+ return -1;
+ }
+
+ int partition = partition(arr, 0, arr.length - 1);
+ while (partition + 1 != k) {
+ if (partition + 1 < k) {
+ partition = partition(arr, partition + 1, arr.length - 1);
+ } else {
+ partition = partition(arr, 0, partition - 1);
+ }
+ }
+
+ return arr[partition];
+ }
+
+ private static int partition(int[] arr, int p, int r) {
+ int pivot = arr[r];
+
+ int i = p;
+ for (int j = p; j <= r - 1; j++) {
+ if (arr[j] < pivot) {
+ swap(arr, i, j);
+ i++;
+ }
+ }
+
+ swap(arr, i, r);
+
+ return i;
+ }
+
+ private static void swap(int[] arr, int i, int j) {
+ if (i == j) {
+ return;
+ }
+
+ int tmp = arr[i];
+ arr[i] = arr[j];
+ arr[j] = tmp;
+ }
+}