mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
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145 lines
15 KiB
JSON
145 lines
15 KiB
JSON
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"questionId": "1661",
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"title": "Minimum Number of Vertices to Reach All Nodes",
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"content": "<p>Given a<strong> directed acyclic graph</strong>, with <code>n</code> vertices numbered from <code>0</code> to <code>n-1</code>, and an array <code>edges</code> where <code>edges[i] = [from<sub>i</sub>, to<sub>i</sub>]</code> represents a directed edge from node <code>from<sub>i</sub></code> to node <code>to<sub>i</sub></code>.</p>\r\n\r\n<p>Find <em>the smallest set of vertices from which all nodes in the graph are reachable</em>. It's guaranteed that a unique solution exists.</p>\r\n\r\n<p>Notice that you can return the vertices in any order.</p>\r\n\r\n<p> </p>\r\n<p><strong>Example 1:</strong></p>\r\n\r\n<p><img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/07/07/untitled22.png\" style=\"width: 231px; height: 181px;\" /></p>\r\n\r\n<pre>\r\n<strong>Input:</strong> n = 6, edges = [[0,1],[0,2],[2,5],[3,4],[4,2]]\r\n<strong>Output:</strong> [0,3]\r\n<b>Explanation: </b>It's not possible to reach all the nodes from a single vertex. From 0 we can reach [0,1,2,5]. From 3 we can reach [3,4,2,5]. So we output [0,3].</pre>\r\n\r\n<p><strong>Example 2:</strong></p>\r\n\r\n<p><img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/07/07/untitled.png\" style=\"width: 201px; height: 201px;\" /></p>\r\n\r\n<pre>\r\n<strong>Input:</strong> n = 5, edges = [[0,1],[2,1],[3,1],[1,4],[2,4]]\r\n<strong>Output:</strong> [0,2,3]\r\n<strong>Explanation: </strong>Notice that vertices 0, 3 and 2 are not reachable from any other node, so we must include them. Also any of these vertices can reach nodes 1 and 4.\r\n</pre>\r\n\r\n<p> </p>\r\n<p><strong>Constraints:</strong></p>\r\n\r\n<ul>\r\n\t<li><code>2 <= n <= 10^5</code></li>\r\n\t<li><code>1 <= edges.length <= min(10^5, n * (n - 1) / 2)</code></li>\r\n\t<li><code>edges[i].length == 2</code></li>\r\n\t<li><code>0 <= from<sub>i,</sub> to<sub>i</sub> < n</code></li>\r\n\t<li>All pairs <code>(from<sub>i</sub>, to<sub>i</sub>)</code> are distinct.</li>\r\n</ul>",
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"code": "class Solution(object):\n def findSmallestSetOfVertices(self, n, edges):\n \"\"\"\n :type n: int\n :type edges: List[List[int]]\n :rtype: List[int]\n \"\"\"\n ",
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"code": "# @param {Integer} n\n# @param {Integer[][]} edges\n# @return {Integer[]}\ndef find_smallest_set_of_vertices(n, edges)\n \nend",
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"code": "impl Solution {\n pub fn find_smallest_set_of_vertices(n: i32, edges: Vec<Vec<i32>>) -> Vec<i32> {\n \n }\n}",
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"A node that does not have any incoming edge can only be reached by itself.",
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"Any other node with incoming edges can be reached from some other node.",
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"We only have to count the number of nodes with zero incoming edges."
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