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http://acm.hdu.edu.cn/showproblem.php?pid=1237
读入一个只包含 +, -, *, / 的非负整数计算表达式,计算该表达式的值。
测试输入包含若干测试用例,每个测试用例占一行,每行不超过200个字符,整数和运算符之间用一个空格分隔。没有非法表达式。当一行中只有0时输入结束,相应的结果不要输出。
对每个测试用例输出1行,即该表达式的值,精确到小数点后2位。
1 + 2
4 + 2 * 5 - 7 / 11
0
3.00
13.36
表达式计算,把前缀表达式变成后缀表达式再计算。。
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<stack>
#include<set>
using std::cin;
using std::sort;
using std::pair;
using std::stack;
using std::string;
using std::getline;
#define pb(e) push_back(e)
#define sz(c) (int)(c).size()
#define mp(a, b) make_pair(a, b)
#define all(c) (c).begin(), (c).end()
#define iter(c) decltype((c).begin())
#define cls(arr, val) memset(arr, val, sizeof(arr))
#define cpresent(c, e) (find(all(c), (e)) != (c).end())
#define rep(i, n) for(int i = 0; i < (int)n; i++)
#define tr(c, i) for(iter(c) i = (c).begin(); i != (c).end(); ++i)
const int N = 5010;
const int INF = 0x3f3f3f3f;
typedef unsigned long long ull;
class ExpCalc {
private:
string ret;
stack<char> op;
stack<double> num;
inline void erase() {
ret = "";
while (!op.empty()) op.pop();
while (!num.empty()) num.pop();
}
inline bool is_digit(char ch) {
return ch >= ‘0‘ && ch <= ‘9‘;
}
inline bool get_op(char ch) {
char buf[10] = "+-*/";
for (int i = 0; i < 4; i++) {
if (buf[i] == ch) return true;
}
return false;
}
inline int cmp(char ch) {
switch (ch) {
case ‘+‘:
case ‘-‘: return 1;
case ‘*‘:
case ‘/‘: return 2;
}
return 0;
}
inline double calc(double d1, double d2, char ch) {
double val = 0.0;
switch (ch) {
case ‘+‘: val = d1 + d2;
break;
case ‘-‘: val = d2 - d1;
break;
case ‘*‘: val = d1 * d2;
break;
case ‘/‘: val = d2 / d1;
break;
}
return val;
}
public:
ExpCalc() { erase(); }
~ExpCalc() { erase(); }
inline void InfixToPostfix(const string src) {
int n = src.length();
for (int i = 0; i < n;) {
if (‘ ‘ == src[i] || ‘=‘ == src[i]) { i++; continue; }
if (‘(‘ == src[i]) op.push(src[i++]);
if (‘)‘ == src[i]) {
while (op.top() != ‘(‘) {
ret += op.top(); ret += ‘ ‘;
op.pop();
}
op.pop(); i++;
} else if (get_op(src[i])) {
while (!op.empty() && cmp(op.top()) >= cmp(src[i])) {
ret += op.top(); ret += ‘ ‘;
op.pop();
}
op.push(src[i++]);
} else {
while (is_digit(src[i]) || ‘.‘ == src[i]) {
ret += src[i++];
}
ret += ‘ ‘;
}
}
while (!op.empty()) {
ret += op.top(); ret += ‘ ‘;
op.pop();
}
ret += ‘=‘;
}
inline double PostfixCalc() {
int n = ret.length();
for (int i = 0; i < n;) {
if (‘ ‘ == ret[i] || ‘=‘ == ret[i]) { i++; continue; }
if (get_op(ret[i])) {
double d1 = num.top(); num.pop();
double d2 = num.top(); num.pop();
num.push(calc(d1, d2, ret[i++]));
} else if (is_digit(ret[i]) || ‘.‘ == ret[i]) {
double x = 0.0;
while (is_digit(ret[i])) {
x = x * 10 + ret[i++] - ‘0‘;
}
if (‘.‘ == ret[i]) {
i++;
double y = 0.0, k = 10.0;
while (is_digit(ret[i])) {
y += (ret[i++] - ‘0‘) / k;
k *= 10;
}
x += y;
}
num.push(x);
}
}
return num.top();
}
};
int main() {
#ifdef LOCAL
freopen("in.txt", "r", stdin);
freopen("out.txt", "w+", stdout);
#endif
string src;
while (getline(cin, src) && src != "0") {
ExpCalc work;
work.InfixToPostfix(src);
printf("%.2lf\n", work.PostfixCalc());
}
return 0;
}
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原文地址:http://www.cnblogs.com/GadyPu/p/4811253.html