【HDOJ】1274 展开字符串

栈的应用，需要注意括号前可能没有数字的情况。

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <stack>
#include <string>
using namespace std;

#define MAXN 300
#define isdigit(c) (c>='0' && c<='9')
#define islower(c) (c>='a' && c<='z')
char str[MAXN];

void solve() {
    string ans = "";
    stack<char> ops;
    stack<int> cnts;
    stack<string> strs;
    int cnt;
    int i = 0;

    while (str[i]) {
        bool found = false;
        cnt = 0;
        while (isdigit(str[i])) {
            cnt = 10*cnt + str[i]-'0';
            ++i;
            found = true;
        }
        if (str[i] == '(') {
            if (!found)
                cnt = 1;
            ops.push('(');
            cnts.push(cnt);
            strs.push(ans);
            ans = "";
        } else if (str[i] == ')') {
            cnt = cnts.top();
            cnts.pop();
            ops.pop();
            int r = cnt;
            string bk = ans;
            ans = strs.top();
            strs.pop();
            while (r) {
                if (r & 1)
                    ans += bk;
                bk += bk;
                r >>= 1;
            }
        } else {
            if (found) {
                string bk(cnt, str[i]);
                ans += bk;
            } else {
                ans += str[i];
            }
        }
        ++i;
    }

    cout <<ans<<endl;
}

int main() {
    int t;
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif
    scanf("%d", &t);
    while (t--) {
        scanf("%s", str);
        solve();
    }

    return 0;
}