Spreadsheet Calculator 电子表格计算器 (Uva 215)

原题:https://uva.onlinejudge.org/external/2/215.pdf

有一个M x N的表格，每个单元格是个数字或者表达式。表达式由单元格编号和＋ － 号组成

输出单元格的结果

思路：用dfs判断有向图环的问题

 #include <iostream>
 #include <cstdio>
 #include <cstdlib>
 #include <utility>
 #include <cstring>
 #include <sstream>

 using namespace std;
 const int MAXR =  + , MAXC =  + ;
 string sheet[MAXR][MAXC];
 int r, c;
 bool hasCircle[MAXR][MAXC], f[MAXR][MAXC], ok;

 bool isNumber(int x, int y) {
     string s = sheet[x][y];
     int l = s.size();
     if (isalpha(s[])) return false;
     for (int i = ; i < l; i++) {
         if (i !=  && !isdigit(s[i])) return false;
     }
     return true;
 }

 void dfs(int x, int y) {
     if (hasCircle[x][y] || isNumber(x, y)) return;
     if (f[x][y]) {hasCircle[x][y] = ; return; }
     f[x][y] = ;
     string s = sheet[x][y];
     char sign; int ans = , right, len = sheet[x][y].size(), i = ;
     while (i < len) {
         sign = '+';
         if (s[i] == '-' || s[i] == '+') {
             sign = s[i];
             i++;
         }
         if (isalpha(s[i])) {
             int nx = s[i] - 'A', ny = s[i + ] - '';
             i += ;
             dfs(nx, ny);
             if (hasCircle[nx][ny]) {
                 hasCircle[x][y] = ;
                 return;
             }
             right = stoi(sheet[nx][ny]);
         }
         else {
             int j = i + ;
             while (j < len && isdigit(s[j])) j++;
             right = stoi(s.substr(i, j - i));
             i = j;
         }
         ans += right * ((sign == '+') ?  : -);
     }
     stringstream ss; ss << ans;
     ss >> sheet[x][y];
 }

 int main() {
     freopen("in", "r", stdin);
     //freopen("out", "w", stdout);
     while (scanf("%d%d", &r, &c) ==  && r) {
         memset(f, , sizeof(f));
         memset(hasCircle, , sizeof(hasCircle));
         ok = ;
         for (int i = ; i < r; i++)
             for (int j = ; j < c; j++)
                 cin >> sheet[i][j];

         for (int i = ; i < r; i++)
             for (int j = ; j < c; j++) {
                 if (!f[i][j])
                     dfs(i, j);
                 if (hasCircle[i][j]) ok = ;
             }
         if (!ok) {
             for (int i = ; i < r; i++)
                 for (int j = ; j < c; j++)
                     if (hasCircle[i][j]) cout << char(i + 'A') << j << ": " << sheet[i][j] << endl;
         }
         else {
             putchar(' ');
             for (int i = ; i < c; i++) printf("     %d", i);
             putchar('\n');
             for (int i = ; i < r; i++) {
                 printf("%c", i + 'A');
                 for (int j = ; j < c; j++) {
                     for (int k = ; k <  - sheet[i][j].size(); k++) putchar(' ');
                     cout << sheet[i][j];
                 }
                 putchar('\n');
             }
         }
         putchar('\n');
     }

     return ;
 }