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[5][105][3];
char str[105];

int dfs(int m, int use, int limit) {
    if(use > K) return 0;
    if(m > n) return use == K;
    if(dp[use][m][limit] != -1) return dp[use][m][limit];
    int up = limit == 1? str[m]-'0':9, ans = 0;
    for(int i = 0; i <= up; ++i)
        ans += dfs(m+1, use+(i!=0), limit&&i==up); 
    return dp[use][m][limit] = ans;
}

void run_case() {
    cin >> (str+1) >> K;
    n = strlen(str+1);
    memset(dp, -1, sizeof(dp));
    cout << dfs(1, 0, 1);
}

int main() {
    ios::sync_with_stdio(false), cin.tie(0);
    //cout.setf(ios_base::showpoint);cout.precision(8);
    run_case();
    cout.flush();
    return 0;
}