找到一组数据的第K大元素

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;
+    }
+}