最简洁代码（14行）

#include<bits/stdc++.h>
using namespace std;
int main() {

  string s, t;
  cin >> s >> t;
  int pos = s.find(t), len = t.size();
  while (pos != -1) {
      s.erase(pos, len);
      int p = max(0, pos - len);
      pos = s.find(t, p);
  }
  cout << s;
  return 0;

}