【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 = ;

     while (str[i]) {
         bool found = false;
         cnt = ;
         while (isdigit(str[i])) {
             cnt = *cnt + str[i]-'';
             ++i;
             found = true;
         }
         if (str[i] == '(') {
             if (!found)
                 cnt = ;
             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 & )
                     ans += bk;
                 bk += bk;
                 r >>= ;
             }
         } 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 ;
 }