URAL - 1057 Amount of Degrees

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题意：求k个不相同的指数的b进制的和在[x, y]中

思路：数位DP，但要注意的是只有系数为1的情况，所以每位只能是0，1，至于不相同的只要是取1 的时候不不相同，至于0是不变的

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
#include <vector>
using namespace std;
const int maxn = 50;

int n, m, b, k;
int num[maxn], dp[maxn][maxn];

int dfs(int cur, int cnt, int flag) {
	if (cur == -1)
		return cnt == k;
	if (!flag && dp[cur][cnt] != -1)
		return dp[cur][cnt];
	int end = flag?num[cur]:b-1;
	int ans = 0;
	for (int i = 0; i <= end && i <= 1; i++) 
		ans += dfs(cur-1, cnt+i, flag&&(i==end)); //+1数才会变化
	if (!flag)
		dp[cur][cnt] = ans;
	return ans;
}

int cal(int x) {
	int len = 0;
	while (x) {
		num[len++] = x%b;
		x /= b;
	}
	return dfs(len-1, 0, 1);
}

int main() {
	memset(dp, -1, sizeof(dp));
	while (scanf("%d%d%d%d", &n, &m, &k, &b) != EOF) {
		int ans = cal(m) - cal(n-1);	
		printf("%d\n", ans);
	}
	return 0;
}

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URAL - 1057 Amount of Degrees

原文：http://blog.csdn.net/u011345136/article/details/38172563