In [1]:
type Node struct {
    child map[byte] *Node // child pointers, key= first char of edge label
    id int
    lab string            // label on edge leading to this node
}
In [2]:
// Return new node with given id and incoming edge label
func NewNode(id int, lab string) *Node {
    node := new (Node)
    node.child = make(map[byte] *Node)
    node.id = id
    node.lab = lab
    return node
}
In [3]:
// Points to particular place in tree; might be partway along an edge
type TreeCursor struct {
    node *Node // node below end of walk
    depth int  // offset along incoming edge
}

// Return null tree cursor
func EmptyTreeCursor() *TreeCursor {
    tc := new (TreeCursor)
    tc.node = nil
    tc.depth = 0
    return tc
}

// Return tree cursor with particular node and offset
func NewTreeCursor(node *Node, depth int) *TreeCursor {
    tc := new (TreeCursor)
    tc.node = node
    tc.depth = depth
    return tc
}
In [4]:
// Suffix tree is simply a root node
type SuffixTree struct {
    root *Node
}

// Construct suffix tree in quadratic time
func NewSuffixTree(t string) *SuffixTree {
    t = t + "$"
    st := new(SuffixTree)
    st.root = NewNode(0, "")
    nextId := 1
    for i := 1; i < len(t); i++ {
        cur := st.root
        j := i
        for j < len(t) {
            c := t[j]
            if child, ok := cur.child[c]; ok {
                k := j+1
                for k - j < len(child.lab) && t[k] == child.lab[k - j] {
                    k++
                }
                if k - j == len(child.lab) { // walked entire edge
                    cur = child
                    j = k
                } else { // new internal node & leaf required
                    cExist := child.lab[k - j]
                    cNew := t[k]
                    mid := NewNode(nextId, t[j:k])
                    mid.child[cNew] = NewNode(nextId + 1, t[k:])
                    nextId += 2
                    mid.child[cExist] = child
                    child.lab = child.lab[k-j:]
                    cur.child[c] = mid
                }
            } else {
                cur.child[c] = NewNode(nextId, t[j:])
                nextId++
            }
        }
    }
    return st
}

// Follow path through tree and return tree cursor from end of walk
func (st *SuffixTree) followPath(s string) *TreeCursor {
    cur := st.root
    for i := 0; i < len(s); {
        c := s[i]
        if child, ok := cur.child[c]; ok {
            j := i + 1
            for j - i < len(child.lab) && j < len(s) && s[j] == child.lab[j - i] {
                j++
            }
            if j - i == len(child.lab) {
                // Exhausted edge; descend
                cur = child
                i = j
            } else if j == len(s) {
                // Exhausted query string in middle of edge
                return NewTreeCursor(child, j-i)
            } else {
                // Fell off in middle of edge
                return EmptyTreeCursor()
            }
        } else {
            return EmptyTreeCursor()
        }
    }
    // Exhausted query string at internal node
    return NewTreeCursor(cur, 0)
}

// Return true iff string has 's' as substring
func (st *SuffixTree) hasSubstring(s string) bool {
    tc := st.followPath(s)
    return tc.node != nil
}

// Return true iff string has 's' as suffix
func (st *SuffixTree) hasSuffix(s string) bool {
    tc := st.followPath(s)
    if tc.node == nil {
        return false
    }
    if tc.depth == 0 {
        _, ok := tc.node.child['$']
        return ok
    } else {
        return tc.node.lab[tc.depth] == '$'
    }
}
In [5]:
stree := NewSuffixTree("there would have been a time for such a word")
In [6]:
stree.hasSubstring("nope")
false
In [7]:
stree.hasSubstring("would have been")
true
In [8]:
stree.hasSubstring("such a word")
true
In [9]:
stree.hasSubstring("")
true
In [10]:
stree.hasSuffix("would have been")
false
In [11]:
stree.hasSuffix("such a word")
true
In [12]:
stree.hasSuffix("")
true