foo.cc: In function 'int main()':
foo.cc:33:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (i = 0; i < v.size(); i++) m[v[i]] = i;
              ~~^~~~~~~~~~
foo.cc:11:12: warning: variable 'j' set but not used [-Wunused-but-set-variable]
  int n, i, j, k;
            ^
foo.cc:11:15: warning: unused variable 'k' [-Wunused-variable]
  int n, i, j, k;
               ^

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