sort2.cpp

C++数值算法原书代码

#include "nr.h"

void NR::sort2(Vec_IO_DP &arr, Vec_IO_DP &brr)
{
	const int M=7,NSTACK=50;
	int i,ir,j,k,jstack=-1,l=0;
	DP a,b;
	Vec_INT istack(NSTACK);

	int n=arr.size();
	ir=n-1;
	for (;;) {
		if (ir-l < M) {
			for (j=l+1;j<=ir;j++) {
				a=arr[j];
				b=brr[j];
				for (i=j-1;i>=l;i--) {
					if (arr[i] <= a) break;
					arr[i+1]=arr[i];
					brr[i+1]=brr[i];
				}
				arr[i+1]=a;
				brr[i+1]=b;
			}
			if (jstack < 0) break;
			ir=istack[jstack--];
			l=istack[jstack--];
		} else {
			k=(l+ir) >> 1;
			SWAP(arr[k],arr[l+1]);
			SWAP(brr[k],brr[l+1]);
			if (arr[l] > arr[ir]) {
				SWAP(arr[l],arr[ir]);
				SWAP(brr[l],brr[ir]);
			}
			if (arr[l+1] > arr[ir]) {
				SWAP(arr[l+1],arr[ir]);
				SWAP(brr[l+1],brr[ir]);
			}
			if (arr[l] > arr[l+1]) {
				SWAP(arr[l],arr[l+1]);
				SWAP(brr[l],brr[l+1]);
			}
			i=l+1;
			j=ir;
			a=arr[l+1];
			b=brr[l+1];
			for (;;) {
				do i++; while (arr[i] < a);
				do j--; while (arr[j] > a);
				if (j < i) break;
				SWAP(arr[i],arr[j]);
				SWAP(brr[i],brr[j]);
			}
			arr[l+1]=arr[j];
			arr[j]=a;
			brr[l+1]=brr[j];
			brr[j]=b;
			jstack += 2;
			if (jstack >= NSTACK) nrerror("NSTACK too small in sort2.");
			if (ir-i+1 >= j-l) {
				istack[jstack]=ir;
				istack[jstack-1]=i;
				ir=j-1;
			} else {
				istack[jstack]=j-1;
				istack[jstack-1]=l;
				l=i;
			}
		}
	}
}