add perm (permutation)

Author: snuke

perm.cpp

@@ -0,0 +1,36 @@
+// Permutation
+// https://youtu.be/-j02o6__jgs?t=7302
+struct Perm : vector<int> {
+#define n (int)(size())
+#define p (*this)
+  Perm(int _n): vector<int>(_n) {
+    iota(begin(), end(), 0);
+  }
+  template<class...Args> Perm(Args...args): vector<int>(args...) {}
+  Perm(initializer_list<int> a): vector<int>(a.begin(),a.end()) {}
+  Perm operator+(const Perm& a) const {
+    Perm r(n);
+    for (int i = 0; i < n; ++i) r[i] = p[a[i]];
+    return r;
+  }
+  Perm& operator+=(const Perm& a) {
+    return *this = (*this)+a;
+  }
+  Perm operator-() const {
+    Perm r(n);
+    for (int i = 0; i < n; ++i) r[p[i]] = i;
+    return r;
+  }
+  Perm operator-(const Perm& a) const {
+    return *this + -a;
+  }
+  Perm& operator-=(const Perm& a) {
+    return *this += -a;
+  }
+  // next permutation
+  bool operator++() {
+    return next_permutation(begin(),end());
+  }
+#undef n
+#undef p
+};