// 802. Find Eventual Safe States #include "leetcode.h" /* * there is a directed graph of 'n' nodes with each node labeled from 0 to n * - 1. the graph is represented by a 0-indexed 2d integer array 'graph' where * 'graph[i]' is an integer array of nodes adjacent to node 'i', meaning there * is an edge from node 'i' to each node in 'graph[i]'. a node is a terminal * node if there are no outgoing edges. a node is a safe node if every possible * path starting from that node leads to a terminal node ( or another safe * node). return an array containing all the safe nodes of the graph. the answer * should be sorted in ascending order. */ class Solution { unordered_set cycle_nodes, safe_nodes; bool dfs(const vvd(int) & graph, int i, unordered_set visited) { if (safe_nodes.find(i) != safe_nodes.end()) return true; if (cycle_nodes.find(i) != cycle_nodes.end()) return false; if (visited.find(i) != visited.end()) { cycle_nodes.insert(i); return false; } visited.insert(i); for (int node : graph[i]) if (!dfs(graph, node, visited)) { cycle_nodes.insert(i); return false; } safe_nodes.insert(i); return true; } public: vector eventualSafeNodes(vvd(int) & graph) { vector ans; unordered_set visited; for (int i = 0; i < graph.size(); i++) if (dfs(graph, i, visited)) ans.push_back(i); return ans; } }; int main() { Solution obj; vvd(int) g1 = {{1, 2}, {2, 3}, {5}, {0}, {5}, {}, {}}; vvd(int) g2 = {{1, 2, 3, 4}, {1, 2}, {3, 4}, {0, 4}, {}}; for (auto i : obj.eventualSafeNodes(g1)) printf("%d ", i); // expect: 2 4 5 6 printf("\n"); for (auto i : obj.eventualSafeNodes(g2)) printf("%d ", i); // expect: 4 printf("\n"); }