spoj ONP - Transform the Expression 中缀转后缀

题目链接

将中缀表达式转化为后缀表达式。

数字的话直接放到答案的字符串里。

如果是左括号就进栈， 右括号就让栈里的符号都出来直到第一个左括号。

否则的话比较当前符号的优先级和栈顶符号的优先级。

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <complex>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <queue>
#include <stack>
#include <bitset>
using namespace std;
#define pb(x) push_back(x)
#define ll long long
#define mk(x, y) make_pair(x, y)
#define lson l, m, rt<<1
#define mem(a) memset(a, 0, sizeof(a))
#define rson m+1, r, rt<<1|1
#define mem1(a) memset(a, -1, sizeof(a))
#define mem2(a) memset(a, 0x3f, sizeof(a))
#define rep(i, n, a) for(int i = a; i<n; i++)
#define fi first
#define se second
typedef complex <double> cmx;
typedef pair<int, int> pll;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int mod = 1e9+7;
const int inf = 1061109567;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
map <char, int> sign;
vector <char> ans;
void solve() {
    ans.clear();
    stack <char> st;
    string s;
    cin>>s;
    int last = 6;
    for(int i = 0; i < s.size(); i++) {
        char c = s[i];
        if(isalnum(c)) {
            ans.pb(c);
        } else {
            if(c == '(') {
                st.push(c);
                last = 6;
            } else if(c == ')') {
                char tmp;
                tmp = st.top();
                st.pop();
                do {
                    ans.pb(tmp);
                    tmp = st.top();
                    st.pop();
                } while (tmp != '(');
                last = 6;
            } else {
                if(sign[c]>=last) {
                    ans.pb(c);
                 } else {
                    st.push(c);
                    last = sign[c];
                 }
            }
        }
    }
    for(auto &i: ans) {
        cout<<i;
    }
    cout<<endl;
}
void init() {
    sign['+'] = 1;
    sign['-'] = 2;
    sign['*'] = 3;
    sign['/'] = 4;
    sign['^'] = 5;
}
int main()
{
    init();
    int t;
    cin>>t;
    while(t--) {
        solve();
    }
    return 0;
}