非递归的归并排序

const int LEN = 20;
void MergeSort(){
	int data[LEN];
	int data2[LEN];
	for(int i=0;i<LEN;++i){
		data[i] = rand()%100;
	}
	for(int i=0;i<LEN;++i)
		cout<<data[i]<<" ";
	cout<<endl;
	int step = 1;
	for(;step<LEN;step *= 2){
		for(int start = 0;start < LEN;start += 2*step){
			int preindex = start;
			int preend = start + step;
			int postindex = start + step;
			int postend = (postindex+step<LEN)?(postindex+step):(LEN);
			int tmpindex = 0;
			while(preindex < preend && postindex < postend){
				if(data[preindex] < data[postindex]){
					data2[tmpindex++] = data[preindex++];
				}
				else{
					data2[tmpindex++] = data[postindex++];
				}
			}
			while(preindex < preend)
				data2[tmpindex++] = data[preindex++];
			while(postindex < postend)
				data2[tmpindex++] = data[postindex++];
			for(int i=0;i<tmpindex;++i)
				data[start+i] = data2[i];
		}
	}
	for(int i=0;i<LEN;++i)
		cout<<data[i]<<" ";
	cout<<endl;
}