SRM 574 D1L2：PolygonTraversal，dp

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题目：http://community.topcoder.com/stat?c=problem_statement&pm=12477&rd=15494

参考：http://apps.topcoder.com/wiki/display/tc/SRM+574

与上一题一样，只是限制条件变成了18，不能再用暴力法了，必须使用dp。

注意位操作，之前在isIntersect()函数中把 if ( mask & (1 << i) ) 写成了 if (mask >> i) ，这个bug调了很久才调出来。

代码：

#include <algorithm>#include <functional>#include <numeric>#include <utility>#include <iostream>#include <sstream>#include <iomanip>#include <bitset>#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>#include <climits>using namespace std;#define CHECKTIME() printf("%.2lf\n", (double)clock() / CLOCKS_PER_SEC)typedef pair<int, int> pii;typedef long long llong;typedef pair<llong, llong> pll;#define mkp make_pair/*************** Program Begin **********************/long long dp[1 << 18][18];class PolygonTraversal {public:int N, start, end;inline int addPoint(int mask, int p){return ( mask | (1 << p) );}bool isIntersect(int mask, int p1, int p2){bool f1 = false, f2 = false;if (p1 > p2) {swap(p1, p2);}for (int i = 0; i < N; i++) {if ( mask & (1 << i) ) {if (i > p1 && i < p2) {f1 = true;} else if (i < p1 || i > p2) {f2 = true;}}}return f1 && f2;}long long rec(int mask, int p){long long & res = dp[mask][p];if (res != -1) {return res;}if (mask == end) {// base caseif (isIntersect(mask, p, start) ) {res = 1;return 1;} else {res = 0;return 0;}}res = 0;for (int i = 0; i < N; i++) {if ( !( mask & (1 << i) ) ) {// 若点未访问if (isIntersect(mask, p, i)) {// 若符合，加入该点res += rec( addPoint(mask, i), i );}}}return res;}long long count(int N, vector <int> points) {long long res = 0;this->N = N;end = (1 << N) - 1;start = points[0] - 1;int mask = 0;for (int i = 0; i < points.size(); i++) {--points[i];mask = addPoint(mask, points[i]);}memset(dp, -1, sizeof(dp));res = rec(mask, points[ points.size() - 1 ]);return res;}};/************** Program End ************************/

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