foo.cc: In function 'bool A(int)':
foo.cc:19:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i=0;i<n;++i) if(k1[i]!=b[i]) o1=0;for(int i=0;i<n;++i) if(k2[i]!=c[i]) o1=0;
  ^~~
foo.cc:19:44: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
  for(int i=0;i<n;++i) if(k1[i]!=b[i]) o1=0;for(int i=0;i<n;++i) if(k2[i]!=c[i]) o1=0;
                                            ^~~
foo.cc:20:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i=0;i<n;++i) if(k2[i]!=b[i]) o2=0;for(int i=0;i<n;++i) if(k1[i]!=c[i]) o2=0;
  ^~~
foo.cc:20:44: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
  for(int i=0;i<n;++i) if(k2[i]!=b[i]) o2=0;for(int i=0;i<n;++i) if(k1[i]!=c[i]) o2=0;
                                            ^~~
foo.cc: In function 'bool B(int)':
foo.cc:34:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i(0);i<n;++i) if(k1[i]!=a[i]) o1=0;for(int i(0);i<n;++i) if(k2[i]!=c[i]) o1=0;
  ^~~
foo.cc:34:45: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
  for(int i(0);i<n;++i) if(k1[i]!=a[i]) o1=0;for(int i(0);i<n;++i) if(k2[i]!=c[i]) o1=0;
                                             ^~~
foo.cc:35:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i(0);i<n;++i) if(k2[i]!=a[i]) o2=0;for(int i(0);i<n;++i) if(k1[i]!=c[i]) o2=0;
  ^~~
foo.cc:35:45: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
  for(int i(0);i<n;++i) if(k2[i]!=a[i]) o2=0;for(int i(0);i<n;++i) if(k1[i]!=c[i]) o2=0;
                                             ^~~
foo.cc: In function 'bool C(int)':
foo.cc:49:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i(0);i<n;++i) if(k1[i]!=b[i]) o1=0;for(int i(0);i<n;++i) if(k2[i]!=a[i]) o1=0;
  ^~~
foo.cc:49:45: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
  for(int i(0);i<n;++i) if(k1[i]!=b[i]) o1=0;for(int i(0);i<n;++i) if(k2[i]!=a[i]) o1=0;
                                             ^~~
foo.cc:50:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i(0);i<n;++i) if(k2[i]!=b[i]) o2=0;for(int i(0);i<n;++i) if(k1[i]!=a[i]) o2=0;
  ^~~
foo.cc:50:45: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
  for(int i(0);i<n;++i) if(k2[i]!=b[i]) o2=0;for(int i(0);i<n;++i) if(k1[i]!=a[i]) o2=0;
                                             ^~~
foo.cc: In function 'int main()':
foo.cc:62:4: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
    for(int i=n-1;i>=0;--i) cout<<a[i];return 0;
    ^~~
foo.cc:62:39: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
    for(int i=n-1;i>=0;--i) cout<<a[i];return 0;
                                       ^~~~~~
foo.cc:65:33: error: 'k' was not declared in this scope
    for(int i=(0);i<n;++i) cout<<k[i];return 0;
                                 ^
foo.cc:65:4: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
    for(int i=(0);i<n;++i) cout<<k[i];return 0;
    ^~~
foo.cc:65:38: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
    for(int i=(0);i<n;++i) cout<<k[i];return 0;
                                      ^~~~~~
foo.cc:68:33: error: 'k' was not declared in this scope
    for(int i=(0);i<n;++i) cout<<k[i];return 0;
                                 ^
foo.cc:68:4: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
    for(int i=(0);i<n;++i) cout<<k[i];return 0;
    ^~~
foo.cc:68:38: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
    for(int i=(0);i<n;++i) cout<<k[i];return 0;
                                      ^~~~~~

自豪的采用 HydroJudge 进行评测(github.com/hydro-dev/HydroJudge)