update at 2021-12-29 00:21:10 by ehlxr

budd-common/src/main/java/io/github/ehlxr/algorithm/FindKthLargest.java

@@ -0,0 +1,123 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright © 2020 xrv <xrg@live.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package io.github.ehlxr.algorithm;
+
+/**
+ * @author ehlxr
+ * @since 2021-12-28 23:16.
+ */
+public class FindKthLargest {
+    public static void main(String[] args) {
+        int[] nums = new int[]{3, 2, 1, 5, 6, 4};
+        System.out.println(findKthLargest(nums, 2));
+    }
+
+    public static int findKthLargest2(int[] nums, int k) {
+        for (int i = nums.length / 2 - 1; i >= 0; i--) {
+            // 从第一个非叶子结点从下至上，从右至左调整结构
+            adjustHeap(nums, i, nums.length);
+        }
+
+        for (int j = nums.length - 1; j >= 0; j--) {
+            k--;
+
+            if (k == 0) {
+                return nums[0];
+            }
+
+            swap(nums, 0, j);
+            adjustHeap(nums, 0, j);
+        }
+
+        return 0;
+    }
+
+    public static void adjustHeap(int[] arr, int i, int length) {
+        // 先取出当前元素 i
+        int temp = arr[i];
+        // 从 i 结点的左子结点开始，也就是 2i+1 处开始
+        for (int k = i * 2 + 1; k < length; k = k * 2 + 1) {
+            // 如果左子结点小于右子结点，k 指向右子结点
+            if (k + 1 < length && arr[k] < arr[k + 1]) {
+                k++;
+            }
+            // 如果子节点大于父节点，将子节点和父节点交换
+            // if (arr[k] > arr[i]) {
+            // swap(arr, k, i);
+            if (arr[k] > temp) {
+                // 不用进行交换
+                arr[i] = arr[k];
+
+                i = k;
+            } else {
+                break;
+            }
+        }
+
+        // 将 temp 值放到最终的位置
+        arr[i] = temp;
+    }
+
+
+    public static int findKthLargest(int[] nums, int k) {
+        if (nums == null || nums.length < k) {
+            return -1;
+        }
+
+        int q = partition(nums, 0, nums.length - 1);
+        while (q + 1 != k) {
+            if (k < q + 1) {
+                q = partition(nums, 0, q - 1);
+            } else {
+                q = partition(nums, q + 1, nums.length - 1);
+            }
+        }
+
+        return nums[q];
+    }
+
+
+    public static int partition(int[] a, int p, int r) {
+        int pivot = a[r];
+        int i = p;
+        for (int j = p; j < r; j++) {
+            if (a[j] >= pivot) {
+                swap(a, i++, j);
+            }
+        }
+
+        swap(a, i, r);
+        return i;
+    }
+
+    private static void swap(int[] a, int i, int j) {
+        if (i == j) {
+            return;
+        }
+        int temp = a[i];
+        a[i] = a[j];
+        a[j] = temp;
+    }
+}

budd-common/src/main/java/io/github/ehlxr/algorithm/sort/QuickSort.java

@@ -32,45 +32,57 @@ import java.util.Arrays;
  */
 public class QuickSort {
     public static void main(String[] args) {
-        int[] arrs = new int[]{3, 2, 5, 7, 1, 9};
-        sort(arrs, 0, arrs.length - 1);
+        int[] a = new int[]{3, 9, 5, 7, 1, 2};
+        sort(a, 0, a.length - 1);
 
-        System.out.println(Arrays.toString(args));
+        System.out.println(Arrays.toString(a));
     }
 
-    public static void sort(int[] arrs, int p, int r) {
+    public static void sort(int[] a, int p, int r) {
         if (p >= r) {
             return;
         }
 
-        int k = partition(arrs, p, r);
+        int q = partition(a, p, r);
 
-        sort(arrs, p, k - 1);
-        sort(arrs, k + 1, r);
+        sort(a, p, q - 1);
+        sort(a, q + 1, r);
     }
 
-    public static int partition(int[] arrs, int p, int r) {
+    /**
+     * 获取分区点
+     * <p>
+     * 图示：https://cdn.jsdelivr.net/gh/0vo/oss/images/quick_sort.jpg
+     * <p>
+     * 通过游标 i 把 a[p...r] 分成两部分。
+     * a[p...i-1] 的元素都是小于 pivot 的，我们暂且叫它 “已处理区间”，a[i...r] 是 “未处理区间”。
+     * 我们每次都从未处理的区间 a[i...r] 中取一个元素 a[j]，与 pivot 对比，
+     * 如果小于 pivot，则将其加入到已处理区间的尾部，也就是 a[i] 的位置
+     * <p>
+     * 只需要将 a[i] 与 a[j] 交换，就可以在 O(1) 时间复杂度内将 a[j] 放到下标为 i 的位置。
+     */
+    public static int partition(int[] a, int p, int r) {
         int i = p;
-        int pivot = arrs[r];
+        int pivot = a[r];
         for (int j = p; j < r; j++) {
-            if (arrs[j] < pivot) {
-                if (j != i) {
-                    swap(arrs, i, j);
-                }
-                i++;
+            if (a[j] < pivot) {
+                swap(a, i++, j);
             }
         }
 
-        swap(arrs, i, r);
-        System.out.println("i=" + i);
+        swap(a, i, r);
+        System.out.println("i=" + i + " " + Arrays.toString(a));
 
         return i;
     }
 
-    public static void swap(int[] arrs, int i, int j) {
-        int temp = arrs[i];
-        arrs[i] = arrs[j];
-        arrs[j] = temp;
+    public static void swap(int[] a, int i, int j) {
+        if (i == j) {
+            return;
+        }
+        int temp = a[i];
+        a[i] = a[j];
+        a[j] = temp;
     }