最大流练习：Parking，二分匹配

来源：互联网发布：ubuntu 16.04应用商店编辑：程序博客网时间：2024/04/30 04:16

题目：http://community.topcoder.com/stat?c=problem_statement&pm=3530&rd=6535

先用BFS求出每辆车到每个停车场的最短距离，接下来就是二分匹配。逐渐增大最小时间D，知道能够找到一条增广路径，若找不到，则说明不能匹配，返回-1。

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 **********************/int g[105][105];bool v_bfs[105][105];int dx[] = {1, -1, 0, 0};int dy[] = {0, 0, 1, -1};const int INF = INT_MAX;int D = 0;const int MAX = 10000;int park_match[105];bool v_dfs[105];class Parking {public:vector <string> park;map <pii, int> car_mp;map <pii, int> park_mp;void BFS(pii start){queue <pair<pii, int>> Q;v_bfs[start.first][start.second] = true;Q.push(mkp(start, 0));while (!Q.empty()) {pii where = Q.front().first;int dist = Q.front().second;Q.pop();if (park_mp.find(where) != park_mp.end()) {g[ car_mp[start] ][ park_mp[where] ] = dist;}for (int i = 0; i < 4; i++) {int nx = where.first + dx[i];int ny = where.second + dy[i];if (nx < 0 || nx >= park.size() || ny < 0 || ny >= park[0].size()) {continue;}if (v_bfs[nx][ny] || 'X' == park[nx][ny]) {continue;}v_bfs[nx][ny] = true;Q.push(mkp( mkp(nx, ny), dist + 1 ));}}}bool DFS(int where){if (-1 == where) {return true;}for (int i = 0; i < park_mp.size(); i++) {if (g[where][i] > D || v_dfs[i]) {continue;}v_dfs[i] = true;if (DFS(park_match[i])) {park_match[i] = where;return true;}}return false;}int minTime(vector <string> park) {int res = 0;this->park = park;int cnt1 = 0, cnt2 = 0;for (int i = 0; i < park.size(); i++) {for (int j = 0; j < park[0].size(); j++) {if ('C' == park[i][j]) {car_mp[mkp(i, j)] = cnt1;++cnt1;} else if ('P' == park[i][j]) {park_mp[mkp(i, j)] = cnt2;++cnt2;}}}for (int i = 0; i < 105; i++) {for (int j = 0; j < 105; j++) {g[i][j] = INF;}}for (map<pii, int>::iterator it = car_mp.begin(); it != car_mp.end(); it++) {memset(v_bfs, 0, sizeof(v_bfs));BFS( (*it).first );}D = 0;memset(park_match, -1, sizeof(park_match));for (int i = 0; i < car_mp.size(); i++) {memset(v_dfs, 0, sizeof(v_dfs));while (D < MAX && !DFS(i)) {++D;memset(v_dfs, 0, sizeof(v_dfs));}if (D >= MAX) {break;}}res = (D >= MAX ? -1 : D);return res;}};/************** Program End ************************/

1 0