URAL 1389 Roadworks

//在一个图中选取尽可能多没有相同结点的边#include <stdio.h>#define MAX 100000typedef struct Road{int to;int next;}Road;Road toArray[MAX * 2];int numOfTos;int toLastAdded[MAX + 1];//degree[city]表示与城市city相连的路中，有可能被封的路的数量int degree[MAX + 1];int queue[MAX + 1];int head, tail;int blocked[MAX + 1];int roadsBlocked[MAX + 1][2];int numOfRoadsBlocked;void addRoad(int from, int to){numOfTos++;int toNum = numOfTos;toArray[toNum].to = to;toArray[toNum].next = toLastAdded[from];toLastAdded[from] = toNum;}int numOfCities, numOfRoads;int main(){freopen("input.txt", "r", stdin);scanf("%d%d", &numOfCities, &numOfRoads);int road;for (road = 1; road <= numOfRoads; road++){int from, to;scanf("%d%d", &from, &to);addRoad(from, to);addRoad(to, from);degree[to]++;degree[from]++;}int city;//先把进出只有一条路的城市给封了，也就是度为1的顶点的连接边给封了for (city = 1; city <= numOfCities; city++)if (degree[city] == 1)queue[tail++] = city;while (head < tail){int cityPoped = queue[head++];if (blocked[cityPoped])continue;blocked[cityPoped] = 1;int cityBlocked = 0;int toIndex;for (toIndex = toLastAdded[cityPoped]; toIndex != 0; toIndex = toArray[toIndex].next){int city = toArray[toIndex].to;if (blocked[city] == 0){blocked[city] = 1;numOfRoadsBlocked++;roadsBlocked[numOfRoadsBlocked][0] = cityPoped;roadsBlocked[numOfRoadsBlocked][1] = city;cityBlocked = city;break;}}if (cityBlocked != 0){for (toIndex = toLastAdded[cityBlocked]; toIndex != 0; toIndex = toArray[toIndex].next){int city = toArray[toIndex].to;if (blocked[city] == 0){//因为城市cityPoped和城市cityBlocked之间的路已经封了，所以城市cityBlocked和城市city之间的路不能再封（因为与城市cityBlocked相连的路最多只能封一条），也就是说在与城市city相连的这些路中，有可能被封的路少了一个，也就是度减1degree[city]--;if (degree[city] == 1)queue[tail++] = city;}}}}printf("%d\n", numOfRoadsBlocked);int roadIndex;for (roadIndex = 1; roadIndex <= numOfRoadsBlocked; roadIndex++)printf("%d %d\n", roadsBlocked[roadIndex][0], roadsBlocked[roadIndex][1]);printf("\n");return 0;}