Quick sort, shell sort

Author: FAREAST\v-wenwli

algs4/src/com/liwenwei/algs4/code/Quick.java

@@ -0,0 +1,64 @@
+/*****************************************************************
+ * Quick sort
+ * 
+ * @author liwenwei
+ * 
+ ****************************************************************/
+package com.liwenwei.algs4.code;
+
+import java.util.Arrays;
+
+public class Quick {
+	
+	private Quick() {
+		
+	}
+	
+	private static int partition(Comparable[] a, int low, int high) {
+		int i = low, j = high + 1;
+		Comparable v = a[low];
+		while (true) {
+			while (less(a[++i], v)) if (i == high) break;
+			while (less(v, a[--j])) if (j == low) break;
+			if (i > j) break;
+			exch(a, i, j);
+		}
+		exch(a, low, j);
+		return j;
+	}
+	
+	public static void sort(Comparable[] a) {
+		sort(a, 0, a.length - 1);
+	}
+	
+	private static void sort(Comparable[] a, int low, int high) {
+		if (low > high) return;
+		int j = partition(a, low, high);
+		sort(a, low, j - 1);
+		sort(a, j + 1, high);
+	}
+	
+	private static boolean less(Comparable v, Comparable w) {
+		return v.compareTo(w) < 0;
+	}
+
+	private static void exch(Comparable[] a, int i, int j) {
+		Comparable t = a[i];
+		a[i] = a[j];
+		a[j] = t;
+	}
+
+	public static boolean isSorted(Comparable[] a) {
+		for (int i = 1; i < a.length; i++) {
+			if (less(a[i], a[i - 1]))
+				return false;
+		}
+		return true;
+	}
+
+	public static void main(String[] args) {
+		Integer[] a = { 6, 4, 10, 9, 7, 7, 8, 10, 8, 9, 10 };
+		Shell.sort(a);
+		System.out.println(Arrays.toString(a));
+	}
+}

java/sort/MergeSort.java

@@ -0,0 +1,57 @@
+package sort;
+
+import java.util.Arrays;
+
+public class MergeSort {
+
+	private static int[] aue;
+
+	private static void merge(int[] arr, int lo, int hi) {
+		int mid = (hi - lo) / 2 + lo;
+		int i = lo;
+		int j = mid + 1;
+		// 复制arr[low, high]到aue
+		for (int k = lo; k <= hi; k++) {
+			aue[k] = arr[k];
+		}
+
+		/*
+		 * 4个判断条件：
+		 * - 左边取完取右边
+		 * - 右边取完取左边
+		 * - 如果左边当前值大于右边当前值，取右边
+		 * - 如果右边当前值大于左边当前值，取左边
+		 */
+		for (int k = lo; k <= hi; k++) {
+			if (i > mid) {
+				arr[k] = aue[j++];
+			} else if (j > hi) {
+				arr[k] = aue[i++];
+			} else if (aue[i] > aue[j]) {
+				arr[k] = aue[j++];
+			} else {
+				arr[k] = aue[i++];
+			}
+		}
+	}
+
+	private static void sort(int[] arr, int lo, int hi) {
+		if (lo >= hi) return;
+		int mid = (hi - lo) / 2 + lo;
+		sort(arr, lo, mid);      // Sort arr[low, mid]
+		sort(arr, mid + 1, hi);  // Sott arr[mid+1, high]
+		merge(arr, lo, hi);
+	}
+
+	public static void sort(int[] arr) {
+		aue = new int[arr.length];
+		sort(arr, 0, arr.length - 1);
+	}
+
+	public static void main(String[] args) {
+		int[] arr = { 2, 1, 5, 9, 4, 3, 2};
+		sort(arr);
+		System.out.println(Arrays.toString(arr));
+	}
+
+}

java/sort/QuickSort.java

@@ -5,6 +5,42 @@
  ***********************************************************************/
 package sort;
 
-public class QuickSort {
+import java.util.Arrays;
 
+public class QuickSort {
+	
+	private static int partition(int[] arr, int lo, int hi) {
+		int pivot = lo;  // pivot
+		int i = lo;      // 左边扫描指针（向右扫描）
+		int j = hi + 1;  // 右边扫描指针（向左扫描）
+		
+		while (true) {
+			// 左右扫描
+			while (arr[pivot] > arr[++i]) if (i == hi) break;
+			while (arr[pivot] < arr[--j]) if (j == lo) break;
+			if (i >= j) break; // 当左右扫描指针相遇时主循环退出
+			swap(arr, i, j);
+		}
+		swap(arr, pivot, j);
+		return j;
+	}
+	
+	private static void swap(int[] arr, int i, int j) {
+		int temp = arr[i];
+		arr[i] = arr[j];
+		arr[j] = temp;
+	}
+	
+	public static void sort(int[] arr, int lo, int hi) {
+		if (lo >= hi) return;
+		int pivot = partition(arr, lo, hi);  // 切分
+		sort(arr, lo, pivot - 1);            // 将左半部分arr[lo .. j-1]排序
+		sort(arr, pivot + 1, hi);            // 将右半部分arr[j+1 .. hi]排序
+	}
+	
+	public static void main(String[] args) {
+		int[] arr = {1, 4, 8, 2, 55, 3, 4, 8, 6, 4, 0, 11, 34, 90, 23, 54, 77, 9, 2, 9, 4, 10};
+		sort(arr, 0, arr.length - 1);
+		System.out.println(Arrays.toString(arr));
+	}
 }

java/sort/ShellSort.java

@@ -0,0 +1,34 @@
+package sort;
+
+import java.util.Arrays;
+
+public class ShellSort {
+
+	public static void sort(int[] arr) {
+		final int len = arr.length;
+		int h = 0;
+		while (h < len) {
+			h = h * 3 + 1;
+		}
+		while (h >= 1) {
+			// insertion sort
+			for (int i = h; i < len; i += h) {
+				for (int j = i; j > 0; j -= h) {
+					if (arr[j] < arr[j - 1]) {
+						int temp = arr[j];
+						arr[j] = arr[j - 1];
+						arr[j - 1] = temp;
+					}
+				}
+			}
+			h /= 3;
+		}
+	}
+
+	public static void main(String[] args) {
+		int[] arr = { 2, 1, 5, 9, 4, 3 };
+		sort(arr);
+		System.out.println(Arrays.toString(arr));
+	}
+
+}