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

storage/zeta/rs/completed/11401.rs

@@ -0,0 +1,44 @@
+use std::io::{read_to_string, stdin};
+
+const MOD: usize = 1_000_000_007;
+
+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 n = iter.next().unwrap();
+    let k = iter.next().unwrap();
+
+    let mut fac = vec![];
+    let mut facinv = vec![];
+
+    fac.push(1);
+    facinv.push(1);
+    fac.push(1);
+    facinv.push(1);
+    for i in 2..=n {
+        let before = fac.last().unwrap();
+        fac.push((before * i) % MOD);
+        facinv.push(get_mod_power(*fac.last().unwrap(), MOD - 2));
+    }
+    let nck = (fac[n] * facinv[n - k] % MOD) * facinv[k] % MOD;
+    println!("{}", nck);
+}