Created
April 12, 2019 21:39
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public class Solution { | |
public int[] FindRedundantDirectedConnection(int[][] edges) | |
{ | |
/* | |
Step 1. Build In and Out Degree map, detect if any any vertex with Multiple parents. | |
Step 2. If we don't find vertex 'A' with multiple parents | |
2.1) Start at 'root' and detect any cycle with DFS, return the edge causing the cycle | |
Step 3. If we find vertex 'A' with multiple parents | |
3.1) if out degree at vertex 'A' is > 0, i.e there is a edge going out of the 'A' vertex | |
3.1.1) Start at 'A' and detect any cycle with DFS, return the edge causing the cycle | |
3.2) if there is NO outgoing edge from vertex 'A' | |
3.2.1) Return the LAST edge that is ending at 'A' (i.e 'A' last parent) | |
*/ | |
var vertexInDegree = new List<int>[edges.Length + 1]; | |
var vertexOutDegree = new List<int>[edges.Length + 1]; | |
for (int i = 0; i < edges.Length + 1; i++) vertexInDegree[i] = new List<int>(); | |
for (int i = 0; i < edges.Length + 1; i++) vertexOutDegree[i] = new List<int>(); | |
bool[] visited = new bool[edges.Length + 1]; // as vertex # starts with 1 | |
int vertexWithMultipleParents = -1; | |
foreach (var arr in edges) | |
{ | |
vertexInDegree[arr[1]].Add(arr[0]); | |
vertexOutDegree[arr[0]].Add(arr[1]); | |
if (vertexInDegree[arr[1]].Count > 1) | |
vertexWithMultipleParents = arr[1]; | |
} | |
if (vertexWithMultipleParents != -1) | |
{ | |
//detect if there is out edges from Vertex with multiple parents | |
//if yes, defect this edge cause a cycle, if yes, remove the first edge | |
//else remove the end edge | |
//start from vertex with multiple parents *********** | |
int root = vertexWithMultipleParents; | |
if (vertexOutDegree[root].Count >0) //if there is a out edge | |
{ | |
Stack<KeyValuePair<int, int>> stack = new Stack<KeyValuePair<int, int>>(); | |
stack.Push(new KeyValuePair<int, int>(root, -1)); | |
while (stack.Any()) | |
{ | |
var node = stack.Pop(); | |
if (!visited[node.Key]) | |
{ | |
visited[node.Key] = true; | |
foreach (int c in vertexOutDegree[node.Key]) | |
stack.Push(new KeyValuePair<int, int>(c, node.Key)); | |
} | |
else | |
{ | |
//cycle detected | |
return new int[] { node.Value, node.Key }; | |
} | |
} | |
return new int[] { vertexInDegree[root][1], root }; | |
} | |
else //doesnt have any out degree, return the last one | |
{ | |
return new int[] { vertexInDegree[root][1], root }; | |
} | |
} | |
else | |
{ | |
//if multple parent vertex NOT found, | |
//then search for cycle, if found, then remove the edge causing the cycle | |
//first edge's as start | |
int root = edges[0][0]; | |
Stack<KeyValuePair<int, int>> stack = new Stack<KeyValuePair<int, int>>(); | |
stack.Push(new KeyValuePair<int, int>(root, -1)); | |
while (stack.Any()) | |
{ | |
var node = stack.Pop(); | |
if (!visited[node.Key]) | |
{ | |
visited[node.Key] = true; | |
foreach (int c in vertexOutDegree[node.Key]) | |
stack.Push(new KeyValuePair<int, int>(c, node.Key)); | |
} | |
else | |
{ | |
//cycle detected | |
return new int[] { node.Value, node.Key}; | |
} | |
} | |
return null; | |
} | |
} | |
} |
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