luogu P2657 [SCOI2009]windy数 数位dp 记忆化搜索

题目链接

luogu P2657 [SCOI2009]windy数

题解

我有了一种所有数位dp都能用记忆话搜索水的错觉

代码

#include<cstdio>
#include<algorithm>
inline int read() {
    int x = 0,f = 1;
    char c = getchar();
    while(c < '0' || c > '9') c = getchar();
    while(c <= '9' && c >= '0') x = x * 10 + c - '0',c = getchar();
    return x * f ;
}
int a,b;
int f[100][100];
int num[100];
int tot;
int dfs(int n,int lim,int pre)  {
    if(n == 0) return 1;
    if(!lim && f[n][pre]) return f[n][pre];
    int sum = 0;
    for(int i = 0;i <= (lim ? num[n] : 9);++ i)  {
        if(i == 0 && pre == -1) sum += dfs(n - 1,lim && i == num[n],-1);
        else if(abs(pre - i) >= 2) sum += dfs(n - 1,lim && i == num[n],i);
    }
    if(!lim) f[n][pre] = sum ;
    return sum;
}
int solve(int x) {
    int tot = 0;
    while(x) num[++ tot] = x % 10,x /= 10;
    return dfs(tot,1,-1);
}
int main() {
    a = read(),b = read();
 	printf("%d\n", solve(b) - solve(a - 1));
 	return 0;
}