归并排序

/*¹é²¢ÅÅÐò*/

#include <iostream>
using namespace std;
void mergeall(int a[],int first,int mid,int end,int t[]){
	int i = first;
	int j = mid+1;
	int k =0;
	while(i<= mid && j <= end){
		if(a[i] <= a[j]){
			t[k++] = a[i++];
		
		}else{
			t[k++] = a[j++];
			
		}
	}
	

		while(j <= end){
			t[k++] = a[j++]; 
		}
	
	
		while(i <= mid){
			t[k++] = a[i++];
	
	}

	for(int m = 0;m <k;m++){
		a[first+m] = t[m];
	}
}
void merge(int a[],int first,int end,int t[]){
	int mid = (first+end)/2;
	
	if(first<end){
	merge(a,first,mid,t);
	merge(a,mid+1,end,t);
	mergeall(a,first,mid,end,t);
	}

}
void mergefirst(int a[],int first,int end){
	int * t = new int[8];

	merge(a,first,end,t);
	delete []t;
}
void main(){
	int a[8] = {3,1,4,2,6,7,9,8};
	mergefirst(a,0,7);
	for(int i =0;i<8;i++){
		cout << a[i];
	}
}

遇到的问题：

一开始没有mergefirst函数，直接在merge函数中new了一个动态数组，但是会导致debug error；

难点：

在于mergeall函数，采用直接插入的方法，复杂度为O(n).

参考：http://blog.youkuaiyun.com/morewindows/article/details/6678165