Added Suffix Tree Implementation in C++ (#261)

Added Suffix Tree Implementation in C++

Author: piyush6348

Trees/Suffix Tree

@@ -0,0 +1,87 @@
+string s;
+int n;
+
+struct node {
+    int l, r, par, link;
+    map<char,int> next;
+
+    node (int l=0, int r=0, int par=-1)
+        : l(l), r(r), par(par), link(-1) {}
+    int len()  {  return r - l;  }
+    int &get (char c) {
+        if (!next.count(c))  next[c] = -1;
+        return next[c];
+    }
+};
+node t[MAXN];
+int sz;
+
+struct state {
+    int v, pos;
+    state (int v, int pos) : v(v), pos(pos)  {}
+};
+state ptr (0, 0);
+
+state go (state st, int l, int r) {
+    while (l < r)
+        if (st.pos == t[st.v].len()) {
+            st = state (t[st.v].get( s[l] ), 0);
+            if (st.v == -1)  return st;
+        }
+        else {
+            if (s[ t[st.v].l + st.pos ] != s[l])
+                return state (-1, -1);
+            if (r-l < t[st.v].len() - st.pos)
+                return state (st.v, st.pos + r-l);
+            l += t[st.v].len() - st.pos;
+            st.pos = t[st.v].len();
+        }
+    return st;
+}
+
+int split (state st) {
+    if (st.pos == t[st.v].len())
+        return st.v;
+    if (st.pos == 0)
+        return t[st.v].par;
+    node v = t[st.v];
+    int id = sz++;
+    t[id] = node (v.l, v.l+st.pos, v.par);
+    t[v.par].get( s[v.l] ) = id;
+    t[id].get( s[v.l+st.pos] ) = st.v;
+    t[st.v].par = id;
+    t[st.v].l += st.pos;
+    return id;
+}
+
+int get_link (int v) {
+    if (t[v].link != -1)  return t[v].link;
+    if (t[v].par == -1)  return 0;
+    int to = get_link (t[v].par);
+    return t[v].link = split (go (state(to,t[to].len()), t[v].l + (t[v].par==0), t[v].r));
+}
+
+void tree_extend (int pos) {
+    for(;;) {
+        state nptr = go (ptr, pos, pos+1);
+        if (nptr.v != -1) {
+            ptr = nptr;
+            return;
+        }
+
+        int mid = split (ptr);
+        int leaf = sz++;
+        t[leaf] = node (pos, n, mid);
+        t[mid].get( s[pos] ) = leaf;
+
+        ptr.v = get_link (mid);
+        ptr.pos = t[ptr.v].len();
+        if (!mid)  break;
+    }
+}
+
+void build_tree() {
+    sz = 1;
+    for (int i=0; i<n; ++i)
+        tree_extend (i);
+}