86 lines
2.1 KiB
Rust
86 lines
2.1 KiB
Rust
/**
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* [2376] Count Special Integers
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*/
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pub struct Solution {}
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// submission codes start here
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use std::collections::HashMap;
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impl Solution {
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pub fn count_special_numbers(n: i32) -> i32 {
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let n: Vec<i32> = n
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.to_string()
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.chars()
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.map(|c| c.to_digit(10).unwrap() as i32)
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.collect();
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let mut result = 0;
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let mut candidate = 9;
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// 计算位数小于n的特殊整数
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for i in 0..n.len() as i32 - 1 {
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result += candidate;
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candidate *= 9 - i
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}
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let mut memory: HashMap<i32, i32> = HashMap::new();
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result += Self::dp(0, false, &mut memory, &n);
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result
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}
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// mask 表示前缀中使用过的数字 使用二进制表示
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// prefix_smaller 当前的前缀是否小于n的前缀
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fn dp(
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mask: i32,
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prefix_smaller: bool,
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memory: &mut HashMap<i32, i32>,
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number: &Vec<i32>,
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) -> i32 {
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let used_bits = mask.count_ones() as usize;
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if used_bits == number.len() {
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return 1;
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}
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let key = mask * 2 + if prefix_smaller { 1 } else { 0 };
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if !memory.contains_key(&key) {
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let mut result = 0;
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let lower_bound = if mask == 0 { 1 } else { 0 };
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let upper_bound = if prefix_smaller { 9 } else { number[used_bits] };
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for i in lower_bound..=upper_bound {
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if mask >> i & 1 == 0 {
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result += Self::dp(
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mask | 1 << i,
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prefix_smaller || i < upper_bound,
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memory,
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number,
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);
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}
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}
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memory.insert(key, result);
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}
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*memory.get(&key).unwrap()
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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_2376() {
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assert_eq!(19, Solution::count_special_numbers(20));
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assert_eq!(5, Solution::count_special_numbers(5));
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assert_eq!(110, Solution::count_special_numbers(135));
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}
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}
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