20240820 Finished
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@ -210,4 +210,5 @@ mod p3117_minimum_sum_of_values_by_dividing_array;
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mod p3137_minimum_number_of_operations_to_make_word_k_periodic;
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mod p3137_minimum_number_of_operations_to_make_word_k_periodic;
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mod p551_student_attendance_record_i;
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mod p551_student_attendance_record_i;
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mod p552_student_attendance_record_ii;
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mod p552_student_attendance_record_ii;
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mod p3154_find_number_of_ways_to_reach_the_k_th_stair;
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@ -0,0 +1,56 @@
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/**
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* [3154] Find Number of Ways to Reach the K-th Stair
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*/
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pub struct Solution {}
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// submission codes start here
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impl Solution {
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pub fn ways_to_reach_stair(k: i32) -> i32 {
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let mut n = 0;
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let mut pos = 1;
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let mut result = 0;
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loop {
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if pos - n - 1 <= k && k <= pos {
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result += Self::combine(n + 1, pos - k);
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}
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if pos - n - 1 > k {
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break;
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}
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n += 1;
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pos *= 2;
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}
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result
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}
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/// C_n^k = \frac{n * (n - 1) * .. * (n - k + 1)}{1 * 2 * 3 * ... * k}
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fn combine(n : i32, k: i32) -> i32 {
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let mut result: i64 = 1;
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let (n, k) = (n as i64, k as i64);
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for i in (n - k + 1..=n).rev() {
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result *= i;
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result /= n - i + 1;
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}
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result as i32
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}
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}
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// submission codes end
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_3154() {
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assert_eq!(2, Solution::ways_to_reach_stair(0));
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assert_eq!(4, Solution::ways_to_reach_stair(1));
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}
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}
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