1851(D,rs): try solving “Prefix Permutation Sums”

Signed-off-by: Matej Focko <me@mfocko.xyz>

1851/src/bin/d.rs

@@ -0,0 +1,223 @@
+#![allow(unused_imports)]
+
+// region ‹use›
+use self::input::*;
+use self::math::*;
+use self::output::*;
+use std::cmp::{max, min};
+use std::collections::HashMap;
+// endregion ‹use›
+
+fn perm_exists(a: Vec<i64>) -> bool {
+    let mut diffs: Vec<i64> = a.iter().zip(a.iter().skip(1)).map(|(y, x)| x - y).collect();
+    diffs.sort();
+
+    dbg!(diffs);
+
+    false
+}
+
+fn solve(s: &mut Scanner) {
+    let n = s.next::<usize>();
+    let prefix = s.next_vec::<i64>(n - 1);
+    yesno(perm_exists(prefix));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn example_1() {
+        assert_eq!(1, 2);
+    }
+}
+
+// region runner
+const SINGLE_TEST: bool = false;
+fn main() {
+    let mut s = Scanner::new();
+
+    if SINGLE_TEST {
+        solve(&mut s)
+    } else {
+        let n = s.next::<usize>();
+        for _ in 0..n {
+            solve(&mut s)
+        }
+    }
+}
+// endregion runner
+
+#[allow(dead_code)]
+mod math {
+    const MOD: i64 = 1_000_000_007;
+
+    pub fn add(a: i64, b: i64) -> i64 {
+        (a + b) % MOD
+    }
+
+    pub fn sub(a: i64, b: i64) -> i64 {
+        ((a - b) % MOD + MOD) % MOD
+    }
+
+    pub fn mul(a: i64, b: i64) -> i64 {
+        (a * b) % MOD
+    }
+
+    pub fn exp(b: i64, e: i64) -> i64 {
+        if e == 0 {
+            return 1;
+        }
+
+        let half = exp(b, e / 2);
+        if e % 2 == 0 {
+            return mul(half, half);
+        }
+
+        mul(half, mul(half, b))
+    }
+
+    /// A trait implementing the unsigned bit shifts.
+    pub trait UnsignedShift {
+        fn unsigned_shl(self, n: u32) -> Self;
+        fn unsigned_shr(self, n: u32) -> Self;
+    }
+
+    /// A trait implementing the integer square root.
+    pub trait ISqrt {
+        fn isqrt(&self) -> Self
+        where
+            Self: Sized,
+        {
+            self.isqrt_checked()
+                .expect("cannot calculate square root of negative number")
+        }
+
+        fn isqrt_checked(&self) -> Option<Self>
+        where
+            Self: Sized;
+    }
+
+    macro_rules! math_traits_impl {
+        ($T:ty, $U: ty) => {
+            impl UnsignedShift for $T {
+                #[inline]
+                fn unsigned_shl(self, n: u32) -> Self {
+                    ((self as $U) << n) as $T
+                }
+
+                #[inline]
+                fn unsigned_shr(self, n: u32) -> Self {
+                    ((self as $U) >> n) as $T
+                }
+            }
+
+            impl ISqrt for $T {
+                #[inline]
+                fn isqrt_checked(&self) -> Option<Self> {
+                    use core::cmp::Ordering;
+                    match self.cmp(&<$T>::default()) {
+                        // Hopefully this will be stripped for unsigned numbers (impossible condition)
+                        Ordering::Less => return None,
+                        Ordering::Equal => return Some(<$T>::default()),
+                        _ => {}
+                    }
+
+                    // Compute bit, the largest power of 4 <= n
+                    let max_shift: u32 = <$T>::default().leading_zeros() - 1;
+                    let shift: u32 = (max_shift - self.leading_zeros()) & !1;
+                    let mut bit = <$T>::try_from(1).unwrap().unsigned_shl(shift);
+
+                    // Algorithm based on the implementation in:
+                    // https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Binary_numeral_system_(base_2)
+                    // Note that result/bit are logically unsigned (even if T is signed).
+                    let mut n = *self;
+                    let mut result = <$T>::default();
+                    while bit != <$T>::default() {
+                        if n >= (result + bit) {
+                            n -= result + bit;
+                            result = result.unsigned_shr(1) + bit;
+                        } else {
+                            result = result.unsigned_shr(1);
+                        }
+                        bit = bit.unsigned_shr(2);
+                    }
+                    Some(result)
+                }
+            }
+        };
+    }
+
+    math_traits_impl!(i8, u8);
+    math_traits_impl!(u8, u8);
+    math_traits_impl!(i16, u16);
+    math_traits_impl!(u16, u16);
+    math_traits_impl!(i32, u32);
+    math_traits_impl!(u32, u32);
+    math_traits_impl!(i64, u64);
+    math_traits_impl!(u64, u64);
+    math_traits_impl!(i128, u128);
+    math_traits_impl!(u128, u128);
+    math_traits_impl!(isize, usize);
+    math_traits_impl!(usize, usize);
+}
+
+#[allow(dead_code)]
+mod output {
+    pub fn yes() {
+        println!("YES");
+    }
+
+    pub fn no() {
+        println!("NO");
+    }
+
+    pub fn yesno(ans: bool) {
+        println!("{}", if ans { "YES" } else { "NO" });
+    }
+}
+
+#[allow(dead_code)]
+mod input {
+    use std::collections::VecDeque;
+    use std::io;
+    use std::str::FromStr;
+
+    pub struct Scanner {
+        buffer: VecDeque<String>,
+    }
+
+    impl Scanner {
+        pub fn new() -> Scanner {
+            Scanner {
+                buffer: VecDeque::new(),
+            }
+        }
+
+        pub fn next<T: FromStr>(&mut self) -> T {
+            if self.buffer.is_empty() {
+                let mut input = String::new();
+
+                io::stdin().read_line(&mut input).ok();
+
+                for word in input.split_whitespace() {
+                    self.buffer.push_back(word.to_string())
+                }
+            }
+
+            let front = self.buffer.pop_front().unwrap();
+            front.parse::<T>().ok().unwrap()
+        }
+
+        pub fn next_vec<T: FromStr>(&mut self, n: usize) -> Vec<T> {
+            let mut arr = vec![];
+
+            for _ in 0..n {
+                arr.push(self.next::<T>());
+            }
+
+            arr
+        }
+    }
+}