解题报告 『[CQOI2016]手机号码（数位动规）』

原题地址

继续用模板水做题。

 

代码实现如下：

//其实本代码有一处地方是多余的,不过我也懒得改了. 
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, a, b) for (register int i = (a); i <= (b); i++)

const int maxn = 15;

int l, r, len;
int num[maxn], dp[(maxn * maxn * maxn) << 3];//数组降维. 

void origin() {memset(dp, -1, sizeof(dp));}

int read() {
    int x = 0, flag = 0;
    char ch = ' ';
    while (ch != '-' && (ch < '0' || ch > '9')) ch = getchar();
    if (ch == '-') {
        flag = 1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = (x << 1) + (x << 3) + ch - '0';
        ch = getchar();
    }
    return flag ? -x : x;
}

int dfs(int pos, int p_pre, int pre, int limit, int lead, int flag, int is_four, int is_eight) {
    int ans = 0;
    if (pos >len) return flag ? 1 : 0;
    if (!limit && !lead && dp[pos * ((maxn * maxn) << 3) + p_pre * (maxn << 3) + (pre << 3) + (flag << 2) + (is_four << 1) + is_eight] != -1) return dp[pos * ((maxn * maxn) << 3) + p_pre * (maxn << 3) + (pre << 3) + (flag << 2) + (is_four << 1) + is_eight];
    int res = limit ? num[len - pos + 1] : 9, ser = lead ? 1 : 0;
    rep(i, ser, res) {
        if (is_four && i == 8) continue;
        if (is_eight && i == 4) continue;
        if (!i && lead) ans += dfs(pos + 1, pre, 0, (i == res) && limit, 1, flag || (i == pre && pre == p_pre), is_four || (i == 4), is_eight || (i == 8));
        else ans += dfs(pos + 1, pre, i, (i == res) && limit, 0, flag || (i == pre && pre == p_pre), is_four || (i == 4), is_eight || (i == 8));
    }
    if (!limit && !lead) dp[pos * ((maxn * maxn) << 3) + p_pre * (maxn << 3) + (pre << 3) + (flag << 2) + (is_four << 1) + is_eight] = ans;
    return ans;
}

int work(int x) {
    origin();
    len = 0;
    while (x) {
        num[++len] = x % 10;
        x /= 10;
    }
    return len != 11 ? 0 : dfs(1, -1, -1, 1, 1, 0, 0, 0);
}

void write(int x) {
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    if (x > 9) write(x / 10);
    putchar(x % 10 + '0');
}

signed main() {
    l = read(), r = read();
    write(work(r) - work(l - 1));
    return 0;
}