gold-4-1

节点间通路。给定有向图，设计一个算法，找出两个节点之间是否存在一条路径。

示例1:

输入：n = 3, graph = [[0, 1], [0, 2], [1, 2], [1, 2]], start = 0, target = 2
输出：true

示例2:

输入：n = 5, graph = [[0, 1], [0, 2], [0, 4], [0, 4], [0, 1], [1, 3], [1, 4], [1, 3], [2, 3], [3, 4]], start = 0, target = 4
输出 true

提示：

1. 节点数量n在[0, 1e5]范围内。
2. 节点编号大于等于 0 小于 n。
3. 图中可能存在自环和平行边。

//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    private boolean[] visited = null;
    public boolean findWhetherExistsPath(int n, int[][] graph, int start, int target) {
        this.visited = new boolean[graph.length];
        return helper(graph, start, target);
    }

    private boolean helper(int[][] graph, int start, int target) {
        for (int i = 0; i < graph.length; ++i) {
            if (!visited[i]) {
                if (graph[i][0] == start && graph[i][1] == target) {
                    return true;
                }
                visited[i] = true;
                if (graph[i][1] == target && helper(graph, start, graph[i][0])) {
                    return true;
                }
                visited[i] = false;
            }
        }
        return false;
    }
}
//leetcode submit region end(Prohibit modification and deletion)