采用分治的思想 以O(NlogN)最坏的情形运行时间运行
如果对merge的每个递归调用都采用局部声明一个临时数组，那么在任一时刻就可能有logN个临时数组处在活动期
代码如下：
1 #include <iostream> 2 #include <vector> 3 using namespace std; 4 template <typename Comparable> 5 void mergeSort(vector<Comparable> & a) 6 { 7 vector<Comparable> tmpArray(a.size()); 8 mergeSort(a,tmpArray,0,a.size()-1); 9 } 10 template <typename Comparable> 11 void mergeSort(vector<Comparable> & a,vector<Comparable> & tmpArray,int left,int right) 12 { 13 if(left<right) 14 { 15 int center = (left+right)/2; 16 mergeSort(a,tmpArray,left,center); 17 mergeSort(a,tmpArray,center+1,right); 18 merge(a,tmpArray,left,center+1,right); 19 } 20 } 21 template <typename Comparable> 22 void merge(vector<Comparable> & a,vector<Comparable> & tmpArray,int leftPos,int rightPos,int rightEnd) 23 { 24 int leftEnd = rightPos-1; 25 int tmpPos = leftPos; 26 int numElements = rightEnd - leftPos + 1; 27 28 while(leftPos <= leftEnd && rightPos <= rightEnd) 29 if(a[leftPos] <= a[rightPos]) 30 tmpArray[tmpPos++] = a[leftPos++]; 31 else 32 tmpArray[tmpPos++] = a[rightPos++]; 33 34 while(leftPos <= leftEnd) 35 tmpArray[tmpPos++] = a[leftPos++]; 36 while(rightPos <= rightEnd) 37 tmpArray[tmpPos++] = a[rightPos++]; 38 39 for(int i=0;i<numElements;i++,rightEnd--) 40 a[rightEnd] = tmpArray[rightEnd]; 41 } 42 int main() 43 { 44 vector<int> ivec; 45 ivec.push_back(1); 46 ivec.push_back(9); 47 ivec.push_back(2); 48 ivec.push_back(10); 49 ivec.push_back(3); 50 ivec.push_back(11); 51 ivec.push_back(4); 52 ivec.push_back(12); 53 ivec.push_back(5); 54 ivec.push_back(13); 55 ivec.push_back(6); 56 ivec.push_back(14); 57 ivec.push_back(7); 58 ivec.push_back(15); 59 ivec.push_back(8); 60 ivec.push_back(16); 61 mergeSort(ivec); 62 for(int j = 0;j<ivec.size();j++) 63 cout<<ivec[j]<<endl; 64 return 0; 65 }
运行结果：
