adding fromLast problem

Author: mamenesia

fromLast/directions.md

@@ -0,0 +1,35 @@
+# --- Directions
+
+Given a linked list and integer 
+spaces from the last node in the
+'size' method of the linked list
+be less than the length of the l
+
+# --- Examples
+   
+    const list = new List();
+    list.insertLast('a');
+    list.insertLast('b');
+    list.insertLast('c');
+    list.insertLast('d');
+    fromLast(list, 2).data // 'b'
+
+
+# --- Solution
+
+    function fromLast(list, n) {
+      let slow = list.getFirst();
+      let fast = list.getFirst();
+
+      while( n > 0) {
+        fast = fast.next;
+        n--;
+      }
+
+      while(fast.next) {
+        slow = slow.next;
+        fast = fast.next;
+      }
+
+      return slow;
+    }

fromLast/fromLast.js

@@ -0,0 +1,31 @@
+// --- Directions
+// Given a linked list and integer 
+// spaces from the last node in the
+// 'size' method of the linked list
+// be less than the length of the l
+// --- Examples
+//    const list = new List();
+//    list.insertLast('a');
+//    list.insertLast('b');
+//    list.insertLast('c');
+//    list.insertLast('d');
+//    fromLast(list, 2).data // 'b'
+
+// Solution
+
+function fromLast(list, n) {
+  let slow = list.getFirst();
+  let fast = list.getFirst();
+
+  while( n > 0) {
+    fast = fast.next;
+    n--;
+  }
+
+  while(fast.next) {
+    slow = slow.next;
+    fast = fast.next;
+  }
+
+  return slow;
+}

fromLast/linkedlist.js

@@ -0,0 +1,164 @@
+// --- Directions
+// Implement classes Node and Linked Lists
+// See 'directions' document
+
+class Node {
+  constructor(data, next = null) {
+    this.data = data;
+    this.next = next;
+  }
+}
+
+class LinkedList {
+  constructor() {
+    this.head = null;
+  }
+
+  insertFirst(data) {
+    // this.head = new Node(data, this.head);
+    this.insertAt(data,0);
+  }
+
+  size() {
+    let counter = 0;
+    let node = this.head;
+    while(node) {
+      counter++;
+      node = node.next;
+    }
+    return counter;
+  }
+
+  getFirst() {
+    // return this.head;
+    return this.getAt(0);
+  }
+
+  getLast() {
+    // if(!this.head) {
+    //   return null;
+    // }
+
+    // let node = this.head;
+    // while(node) {
+    //   if(!node.next) {
+    //     return node;
+    //   }
+    //   node = node.next;
+    // }
+
+    return this.getAt(this.size()-1);
+  }
+
+  clear() {
+    this.head = null;
+  }
+
+  removeFirst() {
+    // if(!this.head) {
+    //   return;
+    // }
+
+    // this.head = this.head.next;
+    this.removeAt(0);
+  }
+
+  removeLast() {
+    
+    // if(!this.head) {
+    //   return;
+    // } else if(!this.head.next) {
+    //   previous = null;
+    //   return;
+    // }
+
+    // let previous = this.head;
+    // let node = this.head.next;
+
+    // while(node.next) {
+    //   previous = node;
+    //   node = node.next;
+    // }
+
+    // previous.next = null;
+
+    this.removeAt(this.size()-1);
+  }
+
+  insertLast(data) {
+    // if(!this.head) {
+    //   this.head = new Node(data);
+    // } else {
+    // this.getLast().next = new Node(data);
+    // }
+    this.insertAt(data, this.size()-1);
+  }
+
+  getAt(index) {
+    let counter = 0;
+    let node = this.head;
+    while(node) {
+      if(counter === index) {
+        return node;
+      }
+      
+      counter++;
+      node = node.next;
+    }
+
+    return null;
+  }
+
+  removeAt(index) {
+    if(!this.head) {
+      return;
+    }
+
+    if(index === 0) {
+      this.head = this.head.next;
+      return;
+    }
+
+    const previous = this.getAt(index-1);
+    if(!previous || !previous.next) {
+      return;
+    }
+    previous.next = previous.next.next;
+  }
+
+  insertAt(data, index) {
+    if(!this.head) {
+      this.head = new Node(data);
+      return;
+    }
+
+    if(index === 0) {
+      this.head = new Node(data, this.head);
+      return;
+    }
+
+    const previous = this.getAt(index-1) || this.getLast();
+    const node = new Node(data, previous.next);
+    previous.next = node;
+  }
+
+  forEach(fn) {
+    let node = this.head;
+    let counter = 0;
+    while (node) {
+      fn(node, counter);
+      node = node.next;
+      counter++;
+    }
+  }
+
+  *[Symbol.iterator]() {
+    let node = this.head;
+    while (node) {
+      yield node;
+      node = node.next;
+    }
+  }
+}
+
+module.exports = { Node, LinkedList };