12_sorts

Author: wangzheng

java/12_sorts/MergeSort.java

@@ -0,0 +1,60 @@
+package sorts;
+
+/**
+ * Created by wangzheng on 2018/10/16.
+ */
+public class MergeSort {
+
+  // 归并排序算法, a是数组，n表示数组大小
+  public static void mergeSort(int[] a, int n) {
+    mergeSortInternally(a, 0, n-1);
+  }
+
+  // 递归调用函数
+  private static void mergeSortInternally(int[] a, int p, int r) {
+    // 递归终止条件
+    if (p >= r) return;
+
+    // 取p到r之间的中间位置q
+    int q = (p+r)/2;
+    // 分治递归
+    mergeSortInternally(a, p, q);
+    mergeSortInternally(a, q+1, r);
+
+    // 将A[p...q]和A[q+1...r]合并为A[p...r]
+    merge(a, p, q, r);
+  }
+
+  private static void merge(int[] a, int p, int q, int r) {
+    int i = p;
+    int j = q+1;
+    int k = 0; // 初始化变量i, j, k
+    int[] tmp = new int[r-p+1]; // 申请一个大小跟a[p...r]一样的临时数组
+    while (i<=q && j<=r) {
+      if (a[i] <= a[j]) {
+        tmp[k++] = a[i++]; // i++等于i:=i+1
+      } else {
+        tmp[k++] = a[j++];
+      }
+    }
+
+    // 判断哪个子数组中有剩余的数据
+    int start = i;
+    int end = q;
+    if (j <= r) {
+      start = j;
+      end = r;
+    }
+
+    // 将剩余的数据拷贝到临时数组tmp
+    while (start <= end) {
+      tmp[k++] = a[start++];
+    }
+
+    // 将tmp中的数组拷贝回a[p...r]
+    for (i = 0; i <= r-p; ++i) {
+      a[p+i] = tmp[i];
+    }
+  }
+
+}

java/12_sorts/QuickSort.java

@@ -0,0 +1,41 @@
+package sorts;
+
+/**
+ * Created by wangzheng on 2018/10/16.
+ */
+public class QuickSort {
+
+  // 快速排序，a是数组，n表示数组的大小
+  public static void quickSort(int[] a, int n) {
+    quickSortInternally(a, 0, n-1);
+  }
+
+  // 快速排序递归函数，p,r为下标
+  private static void quickSortInternally(int[] a, int p, int r) {
+    if (p >= r) return;
+
+    int q = partition(a, p, r); // 获取分区点
+    quickSortInternally(a, p, q-1);
+    quickSortInternally(a, q+1, r);
+  }
+
+  private 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) {
+        int tmp = a[i];
+        a[i] = a[j];
+        a[j] = tmp;
+        ++i;
+      }
+    }
+
+    int tmp = a[i];
+    a[i] = a[r];
+    a[r] = tmp;
+
+    System.out.println("i=" + i);
+    return i;
+  }
+}