ABC154 E - Almost Everywhere Zero

数位DP模板，记忆化+限制即可

#include<bits/stdc++.h>
using namespace std;
#define lowbit(x) ((x)&(-x))
typedef long long LL;

int n, K, dp[][][];
char str[];

int dfs(int m, int use, int limit) {
    if(use > K) return ;
    if(m > n) return use == K;
    if(dp[use][m][limit] != -) return dp[use][m][limit];
    int up = limit == ? str[m]-'':, ans = ;
    for(int i = ; i <= up; ++i)
        ans += dfs(m+, use+(i!=), limit&&i==up);
    return dp[use][m][limit] = ans;
}

void run_case() {
    cin >> (str+) >> K;
    n = strlen(str+);
    memset(dp, -, sizeof(dp));
    cout << dfs(, , );
}

int main() {
    ios::sync_with_stdio(false), cin.tie();
    //cout.setf(ios_base::showpoint);cout.precision(8);
    run_case();
    cout.flush();
    return ;
}