SRM 620 D1L2: CandidatesSelection, Greedy

 题目：http://community.topcoder.com/stat?c=problem_statement&pm=13144&rd=15853

逆向选择，不断剔除条件。

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#define FOREACH(it, X) for(__typeof((X).begin()) it = (X).begin(); it != (X).end(); ++it)/*************** Program Begin **********************/class CandidatesSelection {public:    string possible(vector <string> score, vector <int> result) {vector < pii > cond;int n = result.size();int m = score[0].size();for (int i = 0; i < n - 1; i++) {cond.push_back( mkp(result[i], result[i + 1]) );}bool used[55];memset(used, 0, sizeof(used));while (!cond.empty()) {bool isIndex = true;int r = cond.size();for (int i = 0; i < r; i++) {isIndex &= (cond[i].first < cond[i].second);}if (isIndex) {break;}bool removed = false;for (int i = 0; i < m; i++) {if (used[i]) {continue;}bool ok = true;for (int j = 0; j < r; j++) {ok &= ( score[ cond[j].first ][i] <= score[ cond[j].second ][i] );}if (!ok) {continue;}used[i] = true;vector < pii > newcond;for (int j = 0; j < r; j++) {if (score[ cond[j].first ][i] == score[ cond[j].second ][i]) {newcond.push_back(cond[j]);}}if (newcond.size() == cond.size()) {continue;}removed = true;cond = newcond;break;}if (!removed) {return "Impossible";}}return "Possible";    }};/************** Program End ************************/