complete 11401.rs 13171.rs 13172.rs 13977.rs

storage/zeta/rs/completed/13977.rs

@@ -0,0 +1,55 @@
+use std::io::{BufWriter, Write, read_to_string, stdin, stdout};
+
+const MOD: usize = 1_000_000_007;
+const N_MAX: usize = 4_000_000;
+
+fn get_mod_power(n: usize, p: usize) -> usize {
+    let mut x = p;
+    let mut curr = n % MOD;
+    let mut res = 1;
+    while x > 0 {
+        if x & 1 == 1 {
+            res *= curr;
+            res %= MOD;
+        }
+        x >>= 1;
+        curr *= curr;
+        curr %= MOD;
+    }
+    res
+}
+
+fn main() {
+    let temp = read_to_string(stdin()).unwrap();
+    let mut iter = temp
+        .split_ascii_whitespace()
+        .map(|x| x.parse::<usize>().unwrap());
+
+    let m = iter.next().unwrap();
+
+    let mut fac = vec![0; N_MAX + 1];
+    let mut facinv = vec![0; N_MAX + 1];
+
+    fac[0] = 1;
+    facinv[0] = 1;
+    fac[1] = 1;
+    facinv[1] = 1;
+    for i in 2..=N_MAX {
+        fac[i] = (fac[i - 1] * i) % MOD;
+    }
+
+    facinv[N_MAX] = get_mod_power(fac[N_MAX], MOD - 2);
+    for i in (2..N_MAX).rev() {
+        facinv[i] = facinv[i + 1] * (i + 1) % MOD;
+    }
+
+    let get_nck = |n: usize, k: usize| (fac[n] * facinv[n - k] % MOD) * facinv[k] % MOD;
+
+    let out = stdout();
+    let mut writer = BufWriter::new(out.lock());
+    (0..m).for_each(|_| {
+        let (n, k) = (iter.next().unwrap(), iter.next().unwrap());
+
+        write!(writer, "{}\n", get_nck(n, k)).unwrap();
+    });
+}