add quicksort

src/main/java/me/ehlxr/leetcode/QuickSort.java

@@ -0,0 +1,119 @@
+package me.ehlxr.leetcode;
+
+import java.util.Arrays;
+
+public class QuickSort {
+    /**
+     * 快速排序（左右指针法）
+     *
+     * @param arr  待排序数组
+     * @param low  左边界
+     * @param high 右边界
+     */
+    public static void sort(int[] arr, int low, int high) {
+        if (arr == null || arr.length <= 0) {
+            return;
+        }
+        if (low >= high) {
+            return;
+        }
+
+        int left = low;
+        int right = high;
+
+        int key = arr[left];
+
+        while (left < right) {
+            while (left < right && arr[right] >= key) {
+                right--;
+            }
+            while (left < right && arr[left] <= key) {
+                left++;
+            }
+            if (left < right) {
+                swap(arr, left, right);
+            }
+        }
+        swap(arr, low, left);
+        System.out.println("Sorting: " + Arrays.toString(arr));
+        sort(arr, low, left - 1);
+        sort(arr, left + 1, high);
+    }
+
+    public static void swap(int[] arr, int low, int high) {
+        int tmp = arr[low];
+        arr[low] = arr[high];
+        arr[high] = tmp;
+    }
+
+    /**
+     * 快速排序（挖坑法递归）
+     *
+     * @param arr  待排序数组
+     * @param low  左边界
+     * @param high 右边界
+     */
+    public static void sort2(int[] arr, int low, int high) {
+        if (arr == null || arr.length <= 0) {
+            return;
+        }
+        if (low >= high) {
+            return;
+        }
+
+        int left = low;
+        int right = high;
+        int temp = arr[left]; //挖坑1：保存基准的值
+
+        while (left < right) {
+            while (left < right && arr[right] >= temp) {
+                right--;
+            }
+            arr[left] = arr[right]; //坑2：从后向前找到比基准小的元素，插入到基准位置坑1中
+            while (left < right && arr[left] <= temp) {
+                left++;
+            }
+            arr[right] = arr[left]; //坑3：从前往后找到比基准大的元素，放到刚才挖的坑2中
+        }
+        arr[left] = temp; //基准值填补到坑3中，准备分治递归快排
+        System.out.println("Sorting: " + Arrays.toString(arr));
+        sort2(arr, low, left - 1);
+        sort2(arr, left + 1, high);
+    }
+
+    public static void main(String[] args) {
+        int[] arrs = {2, 4, 7, 5};
+        sort3(arrs, 0, arrs.length - 1);
+    }
+
+    public static void sort3(int[] arr, int l, int r) {
+        if (l >= r) {
+            return;
+        }
+
+        if (arr == null || arr.length <= 0) {
+            return;
+        }
+
+        int i = l, j = r, x = l;
+        int k = arr[x];
+        while (l < r) {
+            while (l < r && arr[r] >= k) {
+                r--;
+            }
+            arr[x] = arr[r];
+            x = r;
+
+            while (l < r && arr[l] <= k) {
+                l++;
+            }
+            arr[x] = arr[l];
+            x = l;
+        }
+        arr[x] = k;
+        System.out.println("Sorting: " + Arrays.toString(arr));
+
+        sort3(arr, i, x - 1);
+        sort3(arr, x + 1, j);
+    }
+}