#[allow(unused_imports)] use std::cmp::*; #[allow(unused_imports)] use std::collections::*; use std::io::*; #[allow(dead_code)] fn getline() -> String { let mut ret = String::new(); std::io::stdin().read_line(&mut ret).ok(); return ret; } fn get_word() -> String { let mut stdin = std::io::stdin(); let mut u8b: [u8; 1] = [0]; loop { let mut buf: Vec = Vec::with_capacity(16); loop { let res = stdin.read(&mut u8b); if res.unwrap_or(0) == 0 || u8b[0] <= b' ' { break; } else { buf.push(u8b[0]); } } if buf.len() >= 1 { let ret = std::string::String::from_utf8(buf).unwrap(); return ret; } } } fn parse(s: &str) -> T { s.parse::().ok().unwrap() } #[allow(dead_code)] fn get() -> T { parse(&get_word()) } /** * Segment Tree. This data structure is useful for fast folding on intervals of an array * whose elements are elements of monoid M. Note that constructing this tree requires the identity * element of M and the operation of M. * Verified by: yukicoder No. 259 (http://yukicoder.me/submissions/100581) */ struct SegTree { n: usize, dat: Vec, op: BiOp, e: I, } impl SegTree where BiOp: Fn(I, I) -> I, I: Copy { pub fn new(n_: usize, op: BiOp, e: I) -> Self { let mut n = 1; while n < n_ { n *= 2; } // n is a power of 2 SegTree {n: n, dat: vec![e; 2 * n - 1], op: op, e: e} } /* ary[k] <- v */ pub fn update(&mut self, idx: usize, v: I) { let mut k = idx + self.n - 1; self.dat[k] = v; while k > 0 { k = (k - 1) / 2; self.dat[k] = (self.op)(self.dat[2 * k + 1], self.dat[2 * k + 2]); } } /* l,r are for simplicity */ fn query_sub(&self, a: usize, b: usize, k: usize, l: usize, r: usize) -> I { // [a,b) and [l,r) intersects? if r <= a || b <= l { return self.e; } if a <= l && r <= b { return self.dat[k]; } let vl = self.query_sub(a, b, 2 * k + 1, l, (l + r) / 2); let vr = self.query_sub(a, b, 2 * k + 2, (l + r) / 2, r); (self.op)(vl, vr) } /* [a, b] (note: inclusive) */ pub fn query(&self, a: usize, b: usize) -> I { self.query_sub(a, b + 1, 0, 0, self.n) } } /** * Union-Find tree. * Verified by yukicoder No.94 (http://yukicoder.me/submissions/82111) */ struct UnionFind { disj: Vec } impl UnionFind { fn new(n: usize) -> Self { let mut disj = vec![0; n]; for i in 0 .. n { disj[i] = i; } UnionFind { disj: disj } } fn root(self: &mut Self, x: usize) -> usize { if x != self.disj[x] { let par = self.disj[x]; let r = self.root(par); self.disj[x] = r; } return self.disj[x]; } fn unite(self: &mut Self, x: usize, y: usize) { let xr = self.root(x); let yr = self.root(y); self.disj[xr] = yr; } fn is_same_set(self: &mut Self, x: usize, y: usize) -> bool { return self.root(x) == self.root(y); } } fn main() { let n = get(); let k: i64 = get(); let d: Vec = (0 .. n).map(|_| get::()).collect(); let mut st = SegTree::new(n + 1, |x, y| x + y, 0i64); let mut uf = UnionFind::new(n); let mut inv: i64 = 0; let mut derange = 0; for i in 0 .. n { inv += st.query(d[i] + 1, n); let tmp = st.query(d[i], d[i]); st.update(d[i], tmp + 1); uf.unite(i, d[i] - 1); } inv %= 2; for i in 0 .. n { if uf.root(i) != i { derange += 1; } } println!("{}", if (k + inv) % 2 == 0 && derange as i64 <= k { "YES" } else { "NO" }); }