2022-10-01：给定一个字符串 s，计算 s 的 不同非空子序列 的个数因为结果可能很大，所以返回答案需要对 10^9 +

use std::collections::HashMap;
fn main() {
    let ans = distinct_subseq_ii("bccaccbaabbc");
    println!("ans = {}", ans);
    let ans = zuo("bccaccbaabbc");
    println!("ans = {}", ans);
}

fn distinct_subseq_ii(s: &str) -> i32 {
    if s.len() == 0 {
        return 0;
    }
    let m = 1000000007;
    let str2: Vec<u8> = s.bytes().collect();
    // a -> 0 ->
    // b -> 1 ->
    // c -> 2 ->
    // z -> 25 ->
    // count[i] = 0
    let mut count = [0; 26];
    // { }
    let mut all = 1; // 算空集
    for x in str2.iter() {
        // x
        // 纯新增
        // add = all - count[x]
        // all += add
        // count[x] + add
        let add = (all - count[(*x - 'a' as u8) as usize] + m) % m;
        all = (all + add) % m;
        count[(*x - 'a' as u8) as usize] = (count[(*x - 'a' as u8) as usize] + add) % m;
    }
    // {} 去掉！
    return all - 1;
}
fn zuo(s: &str) -> i32 {
    if s.len() == 0 {
        return 0;
    }
    let m = 1000000007;
    let str2: Vec<u8> = s.bytes().collect();
    let mut map: HashMap<u8, i32> = HashMap::new();
    let mut all = 1; // 一个字符也没遍历的时候，有空集
    for x in str2.iter() {
        let new_add = all;
        //      int curAll = all + newAdd - (map.containsKey(x) ? map.get(x) : 0);
        let mut cur_all = all;
        cur_all = (cur_all + new_add) % m;
        cur_all = (cur_all
            - if map.contains_key(x) {
                *map.get(x).unwrap()
            } else {
                0
            }
            + m)
            % m;
        all = cur_all;
        map.insert(*x, new_add);
    }
    return all - 1;
}