2025-01-17 归并排序

src/dataANDcalc/java/SortAlgori/MergeSort.java

@@ -0,0 +1,82 @@
+package SortAlgori;
+
+public class MergeSort {
+
+    private int[] arr;
+
+    private int[] temp;
+
+    public MergeSort(int[] arr){
+        this.arr = arr;
+//        this.arr = new int[]{8,4,5,7,1,3,6,2};
+        this.temp = new int[arr.length];
+    }
+
+    public void mergeSort(int left, int right){
+        while(left >= right){
+            return;
+        }
+        int mid = (left + right)/2;
+        mergeSort(left,mid);
+        mergeSort(mid+1,right);
+
+        int leftIndex = left;
+        int rightIndex = mid+1;
+        int index = left;
+        while(index <= right){
+            if(arr[leftIndex] <= arr[rightIndex]){
+                temp[index] = arr[leftIndex];
+                leftIndex ++;
+                index ++;
+            }else{
+                temp[index] = arr[rightIndex];
+                rightIndex ++;
+                index ++;
+            }
+            if(leftIndex > mid){
+                while(rightIndex <= right){
+                    temp[index] = arr[rightIndex];
+                    rightIndex ++;
+                    index ++;
+                }
+                break;
+            }
+            if(rightIndex > right){
+                while(leftIndex <= mid){
+                    temp[index] = arr[leftIndex];
+                    leftIndex ++;
+                    index ++;
+                }
+                break;
+            }
+        }
+
+        for(int i=left; i<=right; i++){
+            arr[i] = temp[i];
+        }
+
+    }
+
+    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] + " ");
+        }
+        MergeSort mergeSort = new MergeSort(arr);
+        long startTime = System.currentTimeMillis();
+        mergeSort.mergeSort(0,arr.length-1);
+        long endTime = System.currentTimeMillis();
+        System.out.println("排序后的序列：");
+        mergeSort.show();
+        System.out.println("排序所花费的时间：" + (endTime - startTime) + "ms");
+    }
+}

src/dataANDcalc/java/SortAlgori/QuickSort.java

@@ -40,11 +40,14 @@ public class QuickSort {
         }
         int leftIndex = left;
         int rightIndex = right;
+        // 以中间的数作为基准
         int mid = arr[(left+right)/2];
         while (leftIndex < rightIndex){
+            // 如果当前左游标小于中间数，则继续往下找，直到找到一个大于mid的数
             while (arr[leftIndex] < mid){
                 leftIndex ++;
             }
+            // 如果当前右游标大于中间数，则继续往上找，直到找到一个小于mid的数
             while (arr[rightIndex] > mid){
                 rightIndex --;
             }
@@ -52,6 +55,7 @@ public class QuickSort {
             if(leftIndex >= rightIndex){
                 break;
             }
+            // 将当前找到左右游标进行一次交换
             swap(leftIndex,rightIndex);
 
             // 如果交换完后发现arr[leftIndex] == mid，rightIndex--，防止出现死循环