20240820 Finished

This commit is contained in:
jackfiled 2024-08-20 11:58:29 +08:00
parent 51c4dc623d
commit f67553296c
2 changed files with 58 additions and 1 deletions

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@ -210,4 +210,5 @@ mod p3117_minimum_sum_of_values_by_dividing_array;
mod p3137_minimum_number_of_operations_to_make_word_k_periodic;
mod p551_student_attendance_record_i;
mod p552_student_attendance_record_ii;
mod p552_student_attendance_record_ii;
mod p3154_find_number_of_ways_to_reach_the_k_th_stair;

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@ -0,0 +1,56 @@
/**
* [3154] Find Number of Ways to Reach the K-th Stair
*/
pub struct Solution {}
// submission codes start here
impl Solution {
pub fn ways_to_reach_stair(k: i32) -> i32 {
let mut n = 0;
let mut pos = 1;
let mut result = 0;
loop {
if pos - n - 1 <= k && k <= pos {
result += Self::combine(n + 1, pos - k);
}
if pos - n - 1 > k {
break;
}
n += 1;
pos *= 2;
}
result
}
/// C_n^k = \frac{n * (n - 1) * .. * (n - k + 1)}{1 * 2 * 3 * ... * k}
fn combine(n : i32, k: i32) -> i32 {
let mut result: i64 = 1;
let (n, k) = (n as i64, k as i64);
for i in (n - k + 1..=n).rev() {
result *= i;
result /= n - i + 1;
}
result as i32
}
}
// submission codes end
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_3154() {
assert_eq!(2, Solution::ways_to_reach_stair(0));
assert_eq!(4, Solution::ways_to_reach_stair(1));
}
}