Add Suffix Tree

README.md

@@ -34,6 +34,9 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
 - [Queue](src/_DataStructures_/Queue)
   - [Weave](src/_DataStructures_/Queue/weave)
 
+- [Suffix Tree](src/_DataStructures_/SuffixTree)
+
+
 ### Logical Problems
 
 - [Anagrams](src/_Problems_/anagrams)

src/_DataStructures_/SuffixTree/index.js

@@ -0,0 +1,121 @@
+/* eslint-disable no-plusplus */
+/*
+Implemented by watching this conceptually video: https://www.youtube.com/watch?v=VA9m_l6LpwI
+
+Suffix for banana are :
+banana
+anana
+nana
+ana
+na
+a
+
+Constructing a suffix tree is O(n*d) where d is length of max string
+
+Searching a suffix of a string is O(d) where d is length of suffix string.
+If found then return the index, else return -1
+
+*/
+
+class Node {
+  constructor(value, isEnd, index) {
+    this.data = value;
+    this.isEnd = isEnd;
+    this.index = index;
+    this.next = new Map();
+  }
+}
+
+class SuffixTree {
+  constructor(string) {
+    this.head = new Node();
+    this.string = string;
+  }
+
+  constructSuffixTree() {
+    const { string } = this;
+    let currentString = '';
+    for (let i = string.length - 1; i >= 0; i -= 1) {
+      currentString = string[i] + currentString;
+      let j = 0;
+      let currentNode = this.head;
+      while (j < currentString.length) {
+        if (!currentNode.next.has(currentString[j])) {
+          currentNode.next.set(currentString[j], new Node(currentString, true, i));
+          break;
+        } else {
+          let k = 0;
+          const partialMatchNode = currentNode.next.get(currentString[j]);
+          const partialMatchString = partialMatchNode.data;
+
+          let matchString = '';
+          while (k < partialMatchString.length && j < currentString.length && partialMatchString[k] === currentString[j]) {
+            matchString += currentString[j];
+            k++;
+            j++;
+          }
+
+          let diffString = '';
+          while (k < partialMatchString.length) {
+            diffString += partialMatchString[k];
+            k++;
+          }
+          partialMatchNode.data = matchString;
+          if (diffString) {
+            partialMatchNode.next.set(diffString[0], new Node(diffString, true, partialMatchNode.index));
+            partialMatchNode.isEnd = false;
+            partialMatchNode.index = null;
+          }
+
+          if (partialMatchNode.next.has(currentString[j])) {
+            currentNode = partialMatchNode;
+          } else {
+            let nextString = '';
+            while (j < currentString.length) {
+              nextString += currentString[j];
+              j++;
+            }
+            partialMatchNode.next.set(nextString[0], new Node(nextString, true, i));
+            break;
+          }
+        }
+      }
+    }
+  }
+
+  findSubstring(string) {
+    if (!this.head.next.has(string[0])) {
+      return -1;
+    }
+
+    let currentNode = this.head.next.get(string[0]);
+    let currentNodeValue = currentNode.data;
+
+    let i = 0; let j = 0;
+
+    while (i < string.length) {
+      j = 0;
+      while (i < string.length && j < currentNodeValue.length && string[i++] === currentNodeValue[j++]);
+
+      if (i === string.length && j === currentNodeValue.length && currentNode.isEnd) {
+        return currentNode.index;
+      }
+
+      if (currentNode.next.has(string[i])) {
+        currentNode = currentNode.next.get(string[i]);
+        currentNodeValue = currentNode.data;
+      } else {
+        return -1;
+      }
+    }
+    return -1;
+  }
+}
+
+// const s = new SuffixTree('banana');
+// s.constructSuffixTree();
+
+//  console.log(s.findSubstring('nana'));
+
+
+module.exports = SuffixTree;