1 #include <cstdio>
 2 #include <vector>
 3 using namespace std;
 4
 5 const int maxn = 1030;
 6
 7 char table[maxn][maxn];
 8
 9 int main()
10 {
11     //freopen("in.txt", "r", stdin);
12
13     int n;
14     while(scanf("%d", &n) == 1 && n)
15     {
16         for(int i = 1; i <= n; i++) scanf("%s", table[i] + 1);
17         vector<int> win, lose;
18         for(int i = 2; i <= n; i++)
19         {
20             if(table[1][i] == '1') win.push_back(i);
21             else lose.push_back(i);
22         }
23
24         int T = n;
25         while(T >>= 1)
26         {
27             vector<int> win2, lose2, final;//进入下一轮1能打败和被打败，以及这一轮混战的队伍
28             bool match;
29             //阶段1:尽可能多的用灰队消灭黑队
30             for(int i = 0; i < lose.size(); i++)
31             {
32                 int black = lose[i];
33                 match = false;
34                 for(int j = 0; j < win.size(); j++)
35                 {
36                     int& gray = win[j];
37                     if(gray > 0 && table[gray][black] == '1')
38                     {
39                         printf("%d %d\n", black, gray);
40                         match = true;
41                         win2.push_back(gray);//灰队进入下一轮
42                         gray = 0;
43                         break;
44                     }
45                 }
46                 if(!match) final.push_back(black);//进入后面的混战
47             }
48             //阶段2:给1队找个对手
49             match = false;
50             for(int i = 0; i < win.size(); i++)
51             {
52                 int team = win[i];
53                 if(team > 0)
54                 {
55                     if(!match) { printf("1 %d\n", team); match = true; }
56                     else final.push_back(team);//1已经匹配到对手，该队进入混战
57                 }
58             }
59             //阶段3:自由混战，注意到黑队在final中都是挨在一起的
60             for(int i = 0; i < final.size(); i += 2)
61             {
62                 printf("%d %d\n", final[i], final[i + 1]);
63                 int survive = final[i];
64                 if(table[final[i + 1]][final[i]] == '1') survive = final[i + 1];
65                 if(table[1][survive] == '1') win2.push_back(survive);
66                 else lose2.push_back(survive);
67             }
68             win = win2;
69             lose = lose2;
70             /*for(int i = 0; i < win.size(); i++) printf("%d ", win[i]);
71             puts("");
72             for(int i = 0; i < lose.size(); i++) printf("%d ", lose[i]);*/
73         }
74     }
75
76     return 0;
77 }