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add perm (permutation)

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	`1`	`+// Permutation`
	`2`	`+// https://youtu.be/-j02o6__jgs?t=7302`
	`3`	`+struct Perm : vector<int> {`
	`4`	`+#define n (int)(size())`
	`5`	`+#define p (*this)`
	`6`	`+ Perm(int _n): vector<int>(_n) {`
	`7`	`+ iota(begin(), end(), 0);`
	`8`	`+ }`
	`9`	`+ template<class...Args> Perm(Args...args): vector<int>(args...) {}`
	`10`	`+ Perm(initializer_list<int> a): vector<int>(a.begin(),a.end()) {}`
	`11`	`+ Perm operator+(const Perm& a) const {`
	`12`	`+ Perm r(n);`
	`13`	`+ for (int i = 0; i < n; ++i) r[i] = p[a[i]];`
	`14`	`+ return r;`
	`15`	`+ }`
	`16`	`+ Perm& operator+=(const Perm& a) {`
	`17`	`+ return this = (this)+a;`
	`18`	`+ }`
	`19`	`+ Perm operator-() const {`
	`20`	`+ Perm r(n);`
	`21`	`+ for (int i = 0; i < n; ++i) r[p[i]] = i;`
	`22`	`+ return r;`
	`23`	`+ }`
	`24`	`+ Perm operator-(const Perm& a) const {`
	`25`	`+ return *this + -a;`
	`26`	`+ }`
	`27`	`+ Perm& operator-=(const Perm& a) {`
	`28`	`+ return *this += -a;`
	`29`	`+ }`
	`30`	`+ // next permutation`
	`31`	`+ bool operator++() {`
	`32`	`+ return next_permutation(begin(),end());`
	`33`	`+ }`
	`34`	`+#undef n`
	`35`	`+#undef p`
	`36`	`+};`

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