View Compilation Error

0_0_30481774_8795.cpp: In function 'void DFS(int, int, int)':
0_0_30481774_8795.cpp:49:12: error: 'a' was not declared in this scope
     if (mn[a] < mn[b]) {
            ^
0_0_30481774_8795.cpp:49:20: error: 'b' was not declared in this scope
     if (mn[a] < mn[b]) {
                    ^
0_0_30481774_8795.cpp:51:18: error: 'ret' was not declared in this scope
                  ret[rt] = l + sz[a];
                  ^
0_0_30481774_8795.cpp:55:6: error: 'ret' was not declared in this scope
      ret[rt] = l + sz[b];
      ^