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import std.stdio:write,writeln; void missing_numbers(int[] arr) { int[int] m; foreach(const ref i;arr) m[i] = i; for(int i = 0; i <= arr.length; ++i) if(i !in m) write(i, ' '); writeln; } void main() { missing_numbers([0,1,3]); missing_numbers([0,1]); }