[Zerojudge]a017: 五則運算

利用stringstream將運算元及運算子以空白隔開，
並一一讀取。

讀到運算元就丟入運算元的堆疊中，
讀到運算子就丟入運算子的堆疊中，
並判斷上一個運算子的優先度是否大於等於它，
若是的話，就一直執行，直到遇到比它小的運算子才放進堆疊中。

唯'('和')'比較特別，
丟入堆疊時：
( > * = / = % > + > - > )，
判斷時：
* = / = % > + > - > ( 。

遇到')'，要一直輸出，只要輸出到'('，就把'('消去，也不把自己')'存進堆疊中。

這樣做完即可得解。

[C++](6ms, 766KB)

	#include<iostream>
	#include<sstream>
	#include<cctype>
	using namespace std;
	int main()
	{
	string s;
	while( getline( cin, s ) )
	{
	string oper;
	stringstream ss;
	char operators[1000] = {0};
	int operands[1000] = {0};
	int operators_length = 0;
	int operands_length = 0;
	ss.clear();
	ss.str(s);
	while( ss >> oper )
	{
	if( isdigit(oper[0]) )
	{
	int number = 0;
	for( int i = 0 ; i < oper.length() ; i++ )
	{
	number *= 10;
	number += oper[i]-'0';
	}
	operands[operands_length++] = number;
	}
	else
	{
	switch( oper[0] )
	{
	case '+': case '-':
	while( operators_length > 0 )
	{
	if( operators[operators_length-1] == '+' )
	{
	operands[operands_length-2] += operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	else if( operators[operators_length-1] == '-' )
	{
	operands[operands_length-2] -= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	else if( operators[operators_length-1] == '*' )
	{
	operands[operands_length-2] *= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	else if( operators[operators_length-1] == '/' )
	{
	operands[operands_length-2] /= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	else if( operators[operators_length-1] == '%' )
	{
	operands[operands_length-2] %= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	else break;
	}
	operators[operators_length++] = oper[0];
	break;
	case '*': case '/': case '%':
	while( operators_length > 0 )
	{
	if( operators[operators_length-1] == '*' )
	{
	operands[operands_length-2] *= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	else if( operators[operators_length-1] == '/' )
	{
	operands[operands_length-2] /= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	else if( operators[operators_length-1] == '%' )
	{
	operands[operands_length-2] %= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	else break;
	}
	operators[operators_length++] = oper[0];
	break;
	case '(':
	operators[operators_length++] = oper[0];
	break;
	case ')':
	for( int i = operators_length-1; operators[i] != '(' ; i-- )
	{
	if( operators[i] == '+' )
	{
	operands[operands_length-2] += operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	if( operators[i] == '-' )
	{
	operands[operands_length-2] -= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	if( operators[i] == '*' )
	{
	operands[operands_length-2] *= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	if( operators[i] == '/' )
	{
	operands[operands_length-2] /= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	if( operators[i] == '%' )
	{
	operands[operands_length-2] %= operands[operands_length-1];
	operands_length--;
	operators_length--;
	}
	}
	operators_length--;
	break;
	}
	}
	}
	for( operators_length-- ; operators_length >= 0 ; operators_length-- )
	{
	if( operators[operators_length] == '+' )
	{
	operands[operands_length-2] += operands[operands_length-1];
	operands_length--;
	}
	if( operators[operators_length] == '-' )
	{
	operands[operands_length-2] -= operands[operands_length-1];
	operands_length--;
	}
	if( operators[operators_length] == '*' )
	{
	operands[operands_length-2] *= operands[operands_length-1];
	operands_length--;
	}
	if( operators[operators_length] == '/' )
	{
	operands[operands_length-2] /= operands[operands_length-1];
	operands_length--;
	}
	if( operators[operators_length] == '%' )
	{
	operands[operands_length-2] %= operands[operands_length-1];
	operands_length--;
	}
	}
	cout << operands[0] << endl;
	}
	return 0;
	}

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