SRM 595 D2 L3：LittleElephantAndXor, dp

题目：http://community.topcoder.com/stat?c=problem_statement&pm=12623&rd=15707

参考：http://apps.topcoder.com/wiki/display/tc/SRM+595

关于位运算的题目应当考虑 逐位 进行dp.

代码：

#include <algorithm>
#include <iostream>
#include <sstream>

#include <string>
#include <vector>
#include <stack>
#include <deque>
#include <queue>
#include <set>
#include <map>

#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <cstring>
#include <ctime>

using namespace std;


#define CHECKTIME() printf("%.2lf\n", (double)clock() / CLOCKS_PER_SEC)

/*************** Program Begin **********************/
long long dp[31][2][2][2];
vector <int> dA, dB, dC;
class LittleElephantAndXor {
public:
	long long rec(int t, int eqA, int eqB, int eqC)
	{

		if (t == -1) {
			return 1;
		}

		long long & res = dp[t][eqA][eqB][eqC];
		if (res != -1) {
			return res;
		}
		res = 0;
		for (int a = 0; a <= 1; a++) {
			for (int b = 0; b <= 1; b++) {
				int eqA2, eqB2, eqC2;
				if (eqA == 1) {
					if (a > dA[t]) {
						continue;
					} else if (a == dA[t]) {
						eqA2 = 1;
					} else {
						eqA2 = 0;
					}
				} else {
					eqA2 = 0;
				}
				if (eqB == 1) {
					if (b > dB[t]) {
						continue;
					} else if (b == dB[t]) {
						eqB2 = 1;
					} else {
						eqB2 = 0;
					}
				} else {
					eqB2 = 0;
				}

				int c = a ^ b;

				if (eqC == 1) {
					if (c > dC[t]) {
						continue;
					} else if (c == dC[t]) {
						eqC2 = 1;
					} else {
						eqC2 = 0;
					}
				} else {
					eqC2 = 0;
				}
				res += rec(t - 1, eqA2, eqB2, eqC2);
			}
		}
		return res;
	}
	long long getNumber(int A, int B, int C) {
		long long res = 0;
		memset(dp, -1, sizeof(dp));
		dA.clear(); dB.clear(); dC.clear();
		for (int i = 0; i < 31; i++) {
			dA.push_back(A & 1);
			dB.push_back(B & 1);
			dC.push_back(C & 1);
			A >>= 1; B >>= 1; C >>= 1;
		}

		res = rec(30, 1, 1, 1);
		return res;
	}

};


/************** Program End ************************/

SRM 595 D2 L3：LittleElephantAndXor, dp

原文：http://blog.csdn.net/xzz_hust/article/details/19052105