[POJ3252]Round Number（数位dp）

题目链接：http://poj.org/problem?id=3252

题意：求范围内数字二进制下0的个数大于等于1的个数的数的个数。

数位dp，dp(l,zero,one,fz)记录当前第l位时0的个数1的个数和当前位是否是前导零中的部分，dfs转移就行。

#include <bits/stdc++.h>
using namespace std;
#define fr first
#define sc second
#define cl clear
#define BUG puts("here!!!")
#define W(a) while(a--)
#define pb(a) push_back(a)
#define Rint(a) scanf("%d", &a)
#define Rll(a) scanf("%I64d", &a)
#define Rs(a) scanf("%s", a)
#define Cin(a) cin >> a
#define FRead() freopen("in", "r", stdin)
#define FWrite() freopen("out", "w", stdout)
#define Rep(i, len) for(int i = 0; i < (len); i++)
#define For(i, a, len) for(int i = (a); i < (len); i++)
#define Cls(a) memset((a), 0, sizeof(a))
#define Clr(a, x) memset((a), (x), sizeof(a))
#define Full(a) memset((a), 0x7f7f7f, sizeof(a))
#define lrt rt << 1
#define rrt rt << 1 | 1
#define pi 3.14159265359
#define RT return
#define lowbit(x) x & (-x)
#define onecnt(x) __builtin_popcount(x)
typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;
typedef pair<int, int> pii;
typedef pair<string, int> psi;
typedef pair<LL, LL> pll;
typedef map<string, int> msi;
typedef vector<int> vi;
typedef vector<LL> vl;
typedef vector<vl> vvl;
typedef vector<bool> vb;

const int maxn = 34;
int digit[maxn];
LL dp[maxn][maxn][maxn][2];

int k;
LL l, r;

LL dfs(int l, int zero, int one, bool fz, bool flag) {
  if(l == 0) return zero >= one;
  if(!flag && ~dp[l][zero][one][fz]) return dp[l][zero][one][fz];
  LL ret = 0;
  int pos = flag ? digit[l] : 1;
  Rep(i, pos+1) {
    if(i == 0 && fz) ret += dfs(l-1, 0, one, fz, flag&&(pos==i));
    else ret += dfs(l-1, zero+(i==0), one+(i==1), false, flag&&(pos==i));
  }
  if(!flag) dp[l][zero][one][fz] = ret;
  return ret;
}

LL f(LL x) {
  int pos = 0;
  while(x) {
    digit[++pos] = x & 1;
    x >>= 1;
  }
  return dfs(pos, 0, 0, true, true);
}

signed main() {
  //FRead();
  Clr(dp, -1);
  while(cin >> l >> r) {
    cout << f(r) - f(l-1) << endl;
  }
  RT 0;
}