2025-01-16 快速排序

src/dataANDcalc/java/SortAlgori/QuickSort.java

@@ -0,0 +1,97 @@
+package SortAlgori;
+
+public class QuickSort {
+
+    private int[] arr;
+
+    public QuickSort(int[] arr){
+//        this.arr = new int[]{238,620,303,470,12,196,635,10,739,12};
+        this.arr = arr;
+    }
+
+    /**
+     * 已最后一个数作为基准(有待完善)
+     */
+    //todo 1.如果基准数重复了 2.完整递归
+    private void tailQuicksort(){
+        int index = 0;
+        int mid = arr[arr.length-1];
+        for(int i=0; i<arr.length-1; i++){
+            if(arr[i]<mid){
+                swap(i,index);
+                index ++;
+            }
+        }
+        swap(index,arr.length-1);
+    }
+
+    /**
+     * 以数组中间的元素作为基准数
+     * @param left
+     * @param right
+     */
+    private void midQuicksort(int left, int right){
+        if(left >= right){
+            return;
+        }
+        int leftIndex = left;
+        int rightIndex = right;
+        int mid = arr[(left+right)/2];
+        while (leftIndex < rightIndex){
+            while (arr[leftIndex] < mid){
+                leftIndex ++;
+            }
+            while (arr[rightIndex] > mid){
+                rightIndex --;
+            }
+            // 如果leftIndex >= rightIndex 说明左边全部是小于mid的数，右边全部是大于mid的数
+            if(leftIndex >= rightIndex){
+                break;
+            }
+            swap(leftIndex,rightIndex);
+
+            // 如果交换完后发现arr[leftIndex] == mid，rightIndex--，防止出现死循环
+            // 这两句判断是当数组中出现重复的数时，有可能会出现重复的数作为mid导致两个mid重复交换死循环
+            if(arr[leftIndex] == mid){
+                rightIndex --;
+            }
+            if(arr[rightIndex] == mid){
+                leftIndex ++;
+            }
+
+        }
+        midQuicksort(left,leftIndex-1);
+        midQuicksort(rightIndex+1,right);
+    }
+
+    private void swap(int i, int j) {
+        int temp = arr[i];
+        arr[i] = arr[j];
+        arr[j] = temp;
+    }
+
+    public void show(){
+        for (int i = 0; i < arr.length; i++) {
+            System.out.print(arr[i] + " ");
+        }
+        System.out.println();
+    }
+
+    public static void main(String[] args) {
+        int[] arr = new int[80000];
+        System.out.println("排序前的序列：");
+        for(int i=0; i<80000; i++){
+            arr[i] = (int)(Math.random()*100000);
+            System.out.print(arr[i] + " ");
+        }
+        QuickSort quickSort = new QuickSort(arr);
+        long startTime = System.currentTimeMillis();
+        quickSort.midQuicksort(0,arr.length-1);
+        long endTime = System.currentTimeMillis();
+        System.out.println("排序后的序列：");
+        quickSort.show();
+        System.out.println("排序所花费的时间：" + (endTime - startTime) + "ms");
+    }
+
+
+}