105 lines
3.5 KiB
Java
105 lines
3.5 KiB
Java
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//给你一个数组 routes ,表示一系列公交线路,其中每个 routes[i] 表示一条公交线路,第 i 辆公交车将会在上面循环行驶。
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//
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//
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// 例如,路线 routes[0] = [1, 5, 7] 表示第 0 辆公交车会一直按序列 1 -> 5 -> 7 -> 1 -> 5 -> 7 -> 1
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//-> ... 这样的车站路线行驶。
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//
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//
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// 现在从 source 车站出发(初始时不在公交车上),要前往 target 车站。 期间仅可乘坐公交车。
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//
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// 求出 最少乘坐的公交车数量 。如果不可能到达终点车站,返回 -1 。
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//
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//
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//
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// 示例 1:
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//
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//
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//输入:routes = [[1,2,7],[3,6,7]], source = 1, target = 6
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//输出:2
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//解释:最优策略是先乘坐第一辆公交车到达车站 7 , 然后换乘第二辆公交车到车站 6 。
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//
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//
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// 示例 2:
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//
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//
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//输入:routes = [[7,12],[4,5,15],[6],[15,19],[9,12,13]], source = 15, target = 12
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//输出:-1
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//
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//
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//
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//
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// 提示:
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//
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//
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// 1 <= routes.length <= 500.
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// 1 <= routes[i].length <= 105
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// routes[i] 中的所有值 互不相同
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// sum(routes[i].length) <= 105
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// 0 <= routes[i][j] < 106
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// 0 <= source, target < 106
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//
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// Related Topics 广度优先搜索 数组 哈希表
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// 👍 149 👎 0
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package leetcode.editor.cn;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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//815:公交路线
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public class BusRoutes {
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public static void main(String[] args) {
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//测试代码
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Solution solution = new BusRoutes().new Solution();
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System.out.println(solution.numBusesToDestination(new int[][]{{1, 2, 7}, {3, 6, 7}}, 1, 6));
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}
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//力扣代码
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//leetcode submit region begin(Prohibit modification and deletion)
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class Solution {
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public int numBusesToDestination(int[][] routes, int source, int target) {
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Map<Integer, List<Integer>> site = new HashMap<>();
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Map<Integer, List<Integer>> bus = new HashMap<>();
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for (int i = 0; i < routes.length; i++) {
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List<Integer> busList = new ArrayList<>();
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for (int j = 0; j < routes[i].length; j++) {
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List<Integer> list = site.getOrDefault(routes[i][j], new ArrayList<>());
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list.add(i);
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site.put(routes[i][j], list);
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busList.add(routes[i][j]);
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}
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bus.put(i, busList);
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}
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int count = minCount(site, bus, source, target, 0, new ArrayList<>());
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return count == Integer.MAX_VALUE ? -1 : count;
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}
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private int minCount(Map<Integer, List<Integer>> map, Map<Integer, List<Integer>> bus, int source, int target, int count, List<Integer> use) {
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if (source == target) {
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return count;
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}
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if (map.get(source).size() == 1 && use.contains(map.get(source).get(0))) {
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return Integer.MAX_VALUE;
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}
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int min = Integer.MAX_VALUE;
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for (int busIndex : map.get(source)) {
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if (use.contains(busIndex)) {
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continue;
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}
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for (int stata : bus.get(busIndex)) {
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if (stata == source) {
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continue;
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}
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use.add(busIndex);
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min = Math.min(min, minCount(map, bus, stata, target, count + 1, use));
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use.remove(use.size() - 1);
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}
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}
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return min;
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}
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}
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//leetcode submit region end(Prohibit modification and deletion)
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}
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