求 1,2,...,n 这n个数字的全部可能的排列.
program lxw006;
const nn=20;
type row=array [1..20] of shortint;
var p: row;
n,i: integer;
num:longint;
procedure wrtperm(n:integer; var s:row);
var i:integer;
begin
for i:=1 to n do write(s[i]:3);
writeln;
end;
procedure perm(n:integer; var p:row; var i:integer);
var j,j1,j2,t,m:integer;
begin
i:=n;
repeat dec(i) until (p[i]<p[i+1]) or (i<1);
if i>0 then
begin
j:=i+1;
for t:=i+1 to n do
if p[i]<p[t] then j:=t;
m:=p[i]; p[i]:=p[j]; p[j]:=m;
t:=(n-i) div 2;
for j:=1 to t do
begin
j1:=i+j; j2:=n-j+1;
m:=p[j1]; p[j1]:=p[j2]; p[j2]:=m;
end;
end;
end;
begin {main}
writeln("输入N:(<=20)"); readln(n);
num:=1;
for i:=1 to n do p[i]:=i;
i:=1;
while i>0 do
begin
wrtperm(n,p);
perm(n,p,i);
if i>0 then inc(num);
end;
writeln("num=",num);
end.
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