# 程序控

IPPP (Institute of Penniless Peasent-Programmer) Fellow

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Time limit: 3.000 seconds

## Background背景

Sorting holds an important place in computer science. Analyzing and implementing various sorting algorithms forms an important part of the education of most computer scientists, and sorting accounts for a significant percentage of the world's computational resources. Sorting algorithms range from the bewilderingly popular Bubble sort, to Quicksort, to parallel sorting algorithms and sorting networks. In this problem you will be writing a program that creates a sorting program (a meta-sorter).

## The Problem问题

The problem is to create several programs whose output is a standard Pascal program that sorts n numbers where n is the only input to the program you will write. The Pascal programs generated by your program must have the following properties:

• They must begin with program sort(input,output);
必须由“program sort(input,output);”开始
• They must declare storage for exactly n integer variables. The names of the variables must come from the first n letters of the alphabet (a,b,c,d,e,f).
必须准确的为n个整形变量声明存储空间。变量名必须按照字母表中的前n个字母排列（a,b,c,d,e,f）。
• A single readln statement must read in values for all the integer variables.
• Other than writeln statements, the only statements in the program are if then else statements. The boolean conditional for each if statement must consist of one strict inequality (either < or >) of two integer variables. Exactly n! writeln statements must appear in the program.
后面除了“writeln”语句外，只能出现“if the else”语句。每个“if”语句的判断条件必须由严格的不等于以前后操作数构成（< 或 >）。程序中必须出现且仅出现n!个writeln语句。
• Exactly three semi-colons must appear in the programs
整个程序中只有三处分号
1. after the program header: program sort(input,output);
在程序头的后面：program sort(input,output);
2. after the variable declaration: ...: integer;
在变量声明的后面：...: integer;
• No redundant comparisons of integer variables should be made. For example, during program execution, once it is determined that a < b, variables a and b should not be compared again.
不要对整型变量做多余的比较。比如在代码运行过程中，一但通过比较确定了a < b，那么a和b这两个变量就不能再次进行比较。
• Every writeln statement must appear on a line by itself.
每条“writeln”语句都独占一行
• The programs must compile. Executing the program with input consisting of any arrangement of any n distinct integer values should result in the input values being printed in sorted order.
输出的代码必须可以编译。执行代码必须能够执行正确的排序运算：输入任意排列的n个值，排序后再输出这n个值。

For those unfamiliar with Pascal syntax, the example at the end of this problem completely defines the small subset of Pascal needed.

## The Input输入

The input consist on a number in the first line indicating the number M of programs to make, followed by a blank line. Then there are M test cases, each one consisting on a single integer n on a line by itself with 1 ≤ n ≤ 8. There will be a blank line between test cases.

## The Output输出

The output is M compilable standard Pascal programs meeting the criteria specified above. Print a blank line between two consecutive programs.

1

3

## Sample Output示例输出

program sort(input,output);
var
a,b,c : integer;
begin
if a < b then
if b < c then
writeln(a,b,c)
else if a < c then
writeln(a,c,b)
else
writeln(c,a,b)
else
if a < c then
writeln(b,a,c)
else if b < c then
writeln(b,c,a)
else
writeln(c,b,a)
end.


## Analysis分析

if c < b then
...
else if c < a then
...
else
...


## Solution

#include <iostream>
#include <string>
using namespace std;
const char *pVars = "abcdefgh";
const char *Indent(int nCnt) {
static const char *pSpaces[] = { "",
"  ", "    ", "      ", "        ", "        ", "          ",
"            ", "              ", "                " };
return pSpaces[nCnt];
}
void MetaSort(int nCurLv, int nMaxLv, string &strOrder) {
if (nCurLv == nMaxLv) {
cout << Indent(nCurLv) << "writeln(" << strOrder[0];
for (size_t i = 1; i < strOrder.size(); ++i) {
cout << ',' << strOrder[i];
}
cout << ")\n";
return;
}
cout << Indent(nCurLv);
for (size_t i = 0; i < strOrder.size(); ++i) {
cout << "if " << pVars[nCurLv] << " < " << strOrder[i] << " then\n";
strOrder.insert(i, pVars + nCurLv, 1);
MetaSort(nCurLv + 1, nMaxLv, strOrder);
strOrder.erase(i, 1);
cout << Indent(nCurLv) << "else ";
}
cout << endl;
strOrder.insert(strOrder.size(), pVars + nCurLv, 1);
MetaSort(nCurLv + 1, nMaxLv, strOrder);
strOrder.erase(strOrder.size() - 1, 1);
}
int main(void) {
int nProgs, nVars;
cin >> nProgs;
for (int j = 0; j < nProgs; ++j) {
cin >> nVars;
if (j != 0) {
cout << endl;
}
string strVarDec = "a";
for (int i = 1; i < nVars; ++i) {
strVarDec.push_back(',');
strVarDec.push_back(i + 'a');
}
cout << "program sort(input,output);\nvar\n" << strVarDec
<< " : integer;\nbegin\n  readln(" << strVarDec << ");\n";
string strInit("a");
MetaSort(1, nVars, strInit);
cout << "end." << endl;
}
return 0;
}

posted on 2010-08-10 03:05  Devymex  阅读(...)  评论(...编辑  收藏