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// 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<int> cycle_nodes, safe_nodes;
bool dfs(const vvd(int) & graph, int i, unordered_set<int> 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<int> eventualSafeNodes(vvd(int) & graph) {
vector<int> ans;
unordered_set<int> 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");
}
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