foo.cc: In function 'int main()':
foo.cc:40:5: error: 'memset' was not declared in this scope
   40 |     memset(ans, -1, sizeof(ans));//初始化
      |     ^~~~~~
foo.cc:4:1: note: 'memset' is defined in header '<cstring>'; did you forget to '#include <cstring>'?
    3 | #include<iostream>
  +++ |+#include <cstring>
    4 | using namespace std;

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