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## Tarjan's algorithm for SCC detection
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```
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UNVISITED = -1
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n = number of nodes in graph
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g = adjacency list with directed edges
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id = 0 # Used to give each node an id
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sccCount = 0 # Used to count number of SCCs found
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# Index i in these arrays represents node i
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ids = [0, 0, ... 0, 0] # Length n
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low = [0, 0, ... 0, 0] # Length n
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onStack = [false, false, ..., false] # Length n
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stack = an empty stack data structure
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function findSccs():
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for(i = 0; i < n; i++): ids[i] = UNVISITED
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for(i = 0; i < n; i++):
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if(ids[i] == UNVISITED):
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dfs(i)
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return low
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function dfs(at):
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stack.push(at)
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onStack[at] = true
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ids[at] = low[at] = id++
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# Visit all neighbours & min low-link on callback
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for(to : g[at]):
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if(ids[to] == UNVISITED): dfs(to)
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if(onStack[to]): low[at] = min(low[at],low[to])
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# After having visited all the neighbours of ‘at’ # if we're at the start of a SCC empty the seen
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# stack until we’re back to the start of the SCC.
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if(ids[at] == low[at]):
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for(node = stack.pop();;node = stack.pop()): onStack[node] = false
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low[node] = ids[at]
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if(node == at): break
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sccCount++
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```
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