归并排序

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归并的思想：

归：就跟分树一样，每次对半分，直到分到1位置

并：从下往上合并,从传入的数组中间分开，左边/右边已经排序好了，此时都从最先结点开始一个一个比大小再合并

要新建一个临时数组

先排序到临时数组再复制回原数组

 #include<stdio.h>#include<stdlib.h>void mergearray(int a[], int first, int mid, int last, int temp[])  {      int i = first;    int j = mid + 1;      int k = 0;            while (i <= mid && j <= last)      {          if (a[i] <= a[j])              temp[k++] = a[i++];          else              temp[k++] = a[j++];      }            while (i <= mid)          temp[k++] = a[i++];            while (j <= last)          temp[k++] = a[j++];            for (i = 0; i < k; i++)  //还原回去,从传入first开始还原        a[first + i] = temp[i];  }  void mergesort(int a[], int first, int last, int temp[]) //临时数组 {      if (first < last)      {          int mid = (first + last) / 2;          mergesort(a, first, mid, temp);    //左边有序          mergesort(a, mid + 1, last, temp); //右边有序          mergearray(a, first, mid, last, temp); //再将二个有序数列合并      }  }    bool MergeSort(int a[], int n)  //排序的接口{      int *p = new int[n];      if (p == NULL)//临时数组          return false;      mergesort(a, 0, n - 1, p);      delete[] p;      return true;  }  int main(){int a[10] = {48,151,13,15,17,18,14,45,46,85};MergeSort(a,10);for(int i=0;i<10;i++){printf("%d ",a[i]);}}

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