PAT 1131. Subway Map (30)

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题目地址：https://www.patest.cn/contests/pat-a-practise/1131

用深搜每次去找路径，每找到一条，就判断是否满足更新的条件，满足就更新

后面的点与前面的点不在同一条地铁线路上就打印换乘

代码中函数的作用，都已经注释好了，如果还有不懂的，欢迎评论~

#include <cstdio>#include <vector>using namespace std;// MAX表示边界，path是用作dfs的临时路径，finalPath是更新之后的最终路径// subway是地铁图// minCnt是经过站的最少次数，minTranf是换成的最少次数，line是图中两点的地铁线号，isVisited是dfs用的标记const int MAX = 10010;vector<int> path, finalPath;vector<vector<int> > subway(MAX);int minCnt = MAX, minTranf = MAX, line[MAX][MAX], isVisited[MAX];// 打印换成路径void printTrace() {    printf("%d\n", minCnt);    int sourceIndex = 0, preLine = line[finalPath[0]][finalPath[1]];    for (int i = 1; i < finalPath.size(); i++) {        int tempLine = line[finalPath[i - 1]][finalPath[i]];        if (tempLine != preLine) {            printf("Take Line#%d from %04d to %04d.\n", preLine, finalPath[sourceIndex], finalPath[i - 1]);            sourceIndex = i - 1;            preLine = tempLine;        }    }    printf("Take Line#%d from %04d to %04d.\n", preLine, finalPath[sourceIndex], finalPath[finalPath.size() - 1]);}// 获取换乘的次数int getTransf(vector<int> a) {    int cnt = 0, preLine = 0;    for (int i = 1; i < a.size(); i++) {        int tempLine = line[a[i - 1]][a[i]];        if (preLine != tempLine) {            cnt++;            preLine = tempLine;        }    }    return cnt;}// 深搜所有的路径，找到目的点的时候，记录将满足题目限制的路径void dfs(int current, int dest, int cnt) {    if (dest == current) {        int tempMinTransf = getTransf(path);        if (cnt < minCnt || (cnt == minCnt && tempMinTransf < minTranf)) {            minCnt = cnt;            finalPath = path;            minTranf = tempMinTransf;        }        return;    }    for (int i = 0; i < subway[current].size(); i++) {        int temp = subway[current][i];        if (!isVisited[temp]) {            isVisited[temp] = true;            path.push_back(temp);            dfs(temp, dest, cnt + 1);            path.pop_back();            isVisited[temp] = false;        }    }}int main() {    int n = 0, k = 0, m = 0, pre = 0, temp = 0, source = 0, dest = 0;    scanf("%d", &n);    for (int i = 1; i <= n; i++) {        scanf("%d %d", &m, &pre);        for (int j = 1; j < m; j++) {            scanf("%d", &temp);            line[temp][pre] = line[pre][temp] = i;            subway[pre].push_back(temp);            subway[temp].push_back(pre);            pre = temp;        }    }    scanf("%d", &k);    for (int i = 0; i < k; i++) {        scanf("%d %d", &source, &dest);        minCnt = MAX;        isVisited[source] = true;        path.push_back(source);        dfs(source, dest, 0);        printTrace();        path.clear();        isVisited[source] = false;        finalPath.clear();    }    return 0;}

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