CODEWITHSUNDEEP
algorithmlanguage-agnosticrecursionstack
tskuzzy
tskuzzy

Reputation: 36446

Translating recursion with globals to iteration using stack

How would you translate a recursive function that uses global variables to an iterative one?

One example of this is using depth-first search where I want to keep track of the path:

path = []

function dfs(node)
    node.visited = true
    path.append(node)

    if node == goal
        print path
        stop;

    for child in node.children
        if !child.visited
            dfs(child)

    path.pop()

How would I do this using iteration and a stack?

Upvotes: 3

Views: 170

Answers (1)

rio
rio

Reputation: 65

If you could extend the Node class, it will be like below.

function iterative_dfs(start_node)
    start_node.next = null
    start_node.visited = true

    stack = []
    stack.push(start_node)

    while !stack.empty?
        node = stack.pop

        if node == goal
            path = []
            while node
                path.push(node)
                node = node.next
            path.reverse
            print path
            stop;

        for child in node.children
            if !child.visited
                child.next = node
                child.visited = true
                stack.push(child)

Also, your code has a bug. You should pop the node if you couldn't find the goal.

function dfs(node)
    node.visited = true
    path.append(node)

    if node == goal
        print path
        stop;

    for child in node.children
        if !child.visited
            dfs(child)

    path.pop    # You need this

Upvotes: 1

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