FZU 2215 Simple Polynomial Problem【模拟】【表达式计算】

题目链接

思路

AC代码

#include <iostream>
#include <cmath>
#include <stack>
#include <string>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long ll;

const int MOD = 1000000007;
struct polynomial
{
ll c[600];
int n;
polynomial()
{
n = 0;
memset(c, 0, sizeof c);
}
friend polynomial operator + (polynomial a, polynomial b)
{
polynomial ans;
int len = max(a.n, b.n);
for (int i = 0; i <= len; ++i)
{
ans.c[i] = a.c[i] + b.c[i];
ans.c[i] %= MOD;
}
ans.n = len;
return ans;
}
friend polynomial operator * (polynomial a, polynomial b)
{
polynomial ans;
if (a.c[a.n] == 0 || b.c[b.n] == 0)
return ans;
for (int i = 0; i <= a.n; ++i)
{
if (i != 0)//每次向右移动一位
{
for (int j = b.n + 1; j >= 1; --j)
{
b.c[j] = b.c[j - 1];
}
b.c[0] = 0;
b.n++;
}
polynomial t = b;
for (int j = 0; j <= b.n; ++j)
{
t.c[j] *= a.c[i];
t.c[j] %= MOD;
}
ans = ans + t;
}
return ans;
}
};

stack <polynomial> st_num;
stack <char> st_op;
void calAB(char op)
{
if (op == '+')
{
st_op.pop();
polynomial a, b;
a = st_num.top(); st_num.pop();
b = st_num.top(); st_num.pop();
st_num.push(a + b);
}
else if (op == '*')
{
st_op.pop();
polynomial a, b;
a = st_num.top(); st_num.pop();
b = st_num.top(); st_num.pop();
st_num.push(a * b);
}
}
polynomial calculate(string s)
{
for (int i = 0; i < s.length(); ++i)
{
if (s[i] == '(' || s[i] == '*')
{
st_op.push(s[i]);
}
else if (s[i] == '+')
{
while (!st_op.empty())
{
if (st_op.top() == '*')
{
calAB('*');
}
else break;
}
st_op.push(s[i]);
}
else if (s[i] == ')')
{
while (!st_op.empty())
{
if (st_op.top() == '*')
{
calAB('*');
}
else if (st_op.top() == '+')
{
calAB('+');
}
else if (st_op.top() == '(')
{
st_op.pop();
break;
}
}
}
else if (isdigit(s[i]))
{
polynomial t;
t.n = 0;
t.c[0] = s[i] - '0';
st_num.push(t);
}
else if (s[i] == 'x')
{
polynomial t;
t.n = 1;
t.c[1] = 1;
st_num.push(t);
}
}
while (!st_op.empty())//最后清算
{
if (st_op.top() == '*')
{
calAB('*');
}
else if (st_op.top() == '+')
{
calAB('+');
}
}
polynomial ans = st_num.top();
while (!st_num.empty())st_num.pop();
while (!st_op.empty())st_op.pop();
return ans;
}
int main()
{
int T;
scanf("%d", &T);
while (T--)
{
string s;
cin >> s;
polynomial ans = calculate(s);
bool flag = 0;
for (int i = ans.n; i >= 0; --i)
{
if (i == ans.n)printf("%lld", ans.c[i]);
else printf(" %lld", ans.c[i]);
}
printf("\n");
}
return 0;
}