ZOJ 3816 Generalized Palindromic Number

一开始觉得是数位DP，后来想不出来。 但是感觉爆搜+剪枝可以过，于是就过了。。

#include <cstdio>
#include <algorithm>
#include <cstring>

using namespace std;
typedef long long LL;
const int maxn = 50;
int lim[maxn], len;
LL num;

void getlim(LL n) {
	memset(lim, 0, sizeof(lim));
	len = 0;
	while (n) {
		lim[len++] = n % 10;
		n /= 10;
	}
}

int tmp[maxn];

bool ok(int len,int rlen) {
	int l = 0, r = len - 1;
	while (l <= r) {
		if (tmp[l] != tmp[r] && r < rlen) return false;
		l++; r--;
	}
	return true;
}

LL dfs(int now, int pos, bool bound, bool first, LL num) {
	if (now == 0) {
		if (ok(pos,pos)) return num;
		else return 0;
	}
	bool can = false;
	for (int j = pos; j <= pos + now; j++) {
		if (ok(j, pos)) {
			can = true; break;
		}
	}
	if (!can) return 0;
	int m = bound ? lim[now - 1] : 9;
	for (int i = m; i >= 0; i--) {
		LL ret;
		int npos = pos;
		if (first || i) {
			if (pos == 0) tmp[pos] = i, npos = 1;
			else {
				if (i != tmp[pos - 1]) {
					tmp[pos] = i;
					npos = pos + 1;
				}
				else npos = pos;
			}
		}
		if (i) ret = dfs(now - 1, npos, bound && i == m, true, num * 10 + i);
		else ret = dfs(now - 1, npos, bound && i == m, false, num * 10 + i);
		if (ret) return ret;
	}
	return 0;
}

int main() {
	memset(f, -1, sizeof(f));
	int T; scanf("%d", &T);
	while (T--) {
		scanf("%lld", &num);
		getlim(num - 1);
		printf("%lld
", dfs(len, 0, 1, 0, 0));
	}
	return 0;
}