1557. Minimum Number of Vertices to Reach All Nodes: AC

Author: tan-wei

src/solution/mod.rs

@@ -1173,3 +1173,4 @@ mod s1551_minimum_operations_to_make_array_equal;
 mod s1552_magnetic_force_between_two_balls;
 mod s1553_minimum_number_of_days_to_eat_n_oranges;
 mod s1556_thousand_separator;
+mod s1557_minimum_number_of_vertices_to_reach_all_nodes;

src/solution/s1557_minimum_number_of_vertices_to_reach_all_nodes.rs

@@ -0,0 +1,78 @@
+/**
+ * [1557] Minimum Number of Vertices to Reach All Nodes
+ *
+ * Given a directed acyclic graph, with n vertices numbered from 0 to n-1, and an array edges where edges[i] = [fromi, toi] represents a directed edge from node fromi to node toi.
+ * Find the smallest set of vertices from which all nodes in the graph are reachable. It's guaranteed that a unique solution exists.
+ * Notice that you can return the vertices in any order.
+ *  
+ * Example 1:
+ * <img alt="" src="https://assets.leetcode.com/uploads/2020/07/07/untitled22.png" style="width: 231px; height: 181px;" />
+ *
+ * Input: n = 6, edges = [[0,1],[0,2],[2,5],[3,4],[4,2]]
+ * Output: [0,3]
+ * Explanation: 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].
+ * Example 2:
+ * <img alt="" src="https://assets.leetcode.com/uploads/2020/07/07/untitled.png" style="width: 201px; height: 201px;" />
+ *
+ * Input: n = 5, edges = [[0,1],[2,1],[3,1],[1,4],[2,4]]
+ * Output: [0,2,3]
+ * Explanation: 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.
+ *
+ *  
+ * Constraints:
+ *
+ * 	2 <= n <= 10^5
+ * 	1 <= edges.length <= min(10^5, n * (n - 1) / 2)
+ * 	edges[i].length == 2
+ * 	0 <= fromi, toi < n
+ * 	All pairs (fromi, toi) are distinct.
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/minimum-number-of-vertices-to-reach-all-nodes/
+// discuss: https://leetcode.com/problems/minimum-number-of-vertices-to-reach-all-nodes/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    pub fn find_smallest_set_of_vertices(n: i32, edges: Vec<Vec<i32>>) -> Vec<i32> {
+        use std::iter::FromIterator;
+
+        let mut set: std::collections::HashSet<i32> =
+            std::collections::HashSet::from_iter((0..n).into_iter());
+
+        for edge in edges {
+            set.remove(&edge[1]);
+        }
+
+        set.into_iter().collect::<Vec<i32>>()
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1557_example_1() {
+        let n = 6;
+        let edges = vec![vec![0, 1], vec![0, 2], vec![2, 5], vec![3, 4], vec![4, 2]];
+
+        let result = vec![0, 3];
+
+        assert_eq_sorted!(Solution::find_smallest_set_of_vertices(n, edges), result)
+    }
+
+    #[test]
+    fn test_1557_example_2() {
+        let n = 5;
+        let edges = vec![vec![0, 1], vec![2, 1], vec![3, 1], vec![1, 4], vec![2, 4]];
+
+        let result = vec![0, 2, 3];
+
+        assert_eq_sorted!(Solution::find_smallest_set_of_vertices(n, edges), result)
+    }
+}