[Function add]

1. Add leetcode solutions with tag amazon tag.

Author: Seanforfun

Diff for: leetcode/117. Populating Next Right Pointers in Each Node II.md

@@ -105,4 +105,32 @@ public class Solution {
         }
     }
 }
-```
+```
+
+### Amazon session
+* Method 1: BFS using recursion Space complexity O(1).
+	```Java
+	class Solution {
+		public Node connect(Node root) {
+			recursion(root);
+			return root;
+		}
+		private void recursion(Node node){
+			if(node == null) return;
+			Node dummy = new Node();
+			Node cur = dummy;
+			while(node != null){	// for current level.
+				if(node.left != null){	// append all child nodes.
+					cur.next = node.left;
+					cur = cur.next;
+				}
+				if(node.right != null){
+					cur.next = node.right;
+					cur = cur.next;
+				}
+				node = node.next;
+			}
+			recursion(dummy.next);	// recursion to next level.
+		}
+	}
+	```

Diff for: leetcode/284. Peeking Iterator.md

@@ -99,3 +99,43 @@ class PeekingIterator implements Iterator<Integer> {
 	}
 }
 ```
+
+### Amazon session
+* Method 1: use a peek holder instead of a list.
+	```Java
+	// Java Iterator interface reference:
+	// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
+	class PeekingIterator implements Iterator<Integer> {
+		private Integer peek;
+		private Iterator<Integer> it;
+		public PeekingIterator(Iterator<Integer> iterator) {
+			// initialize any member here.	    
+			this.it = iterator;
+		}
+
+		// Returns the next element in the iteration without advancing the iterator.
+		public Integer peek() {
+			if(peek == null) {
+				peek = it.next();
+			}
+			return peek;
+		}
+
+		// hasNext() and next() should behave the same as in the Iterator interface.
+		// Override them if needed.
+		@Override
+		public Integer next() {
+			if(peek == null) return it.next();
+			else{
+				Integer res = new Integer(peek);
+				peek = null;
+				return res;
+			}
+		}
+
+		@Override
+		public boolean hasNext() {
+			return peek != null || it.hasNext();
+		}
+	}
+	```

Diff for: leetcode/706. Design HashMap.md

@@ -127,4 +127,34 @@ Note:
      * int param_2 = obj.get(key);
      * obj.remove(key);
      */
-    ```
+    ```
+
+### Amazon Session
+* Method 1: 
+	```Java
+	class MyHashMap {
+		private int[] values;
+		private static final int LEN = 1000001;
+		/** Initialize your data structure here. */
+		public MyHashMap() {
+			this.values = new int[LEN];
+			Arrays.fill(this.values, -1);
+		}
+		
+		/** value will always be non-negative. */
+		public void put(int key, int value) {
+			int index = new Integer(key).hashCode() % LEN;
+			this.values[index] = value;
+		}
+		
+		/** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
+		public int get(int key) {
+			return this.values[new Integer(key).hashCode() % LEN];
+		}
+		
+		/** Removes the mapping of the specified value key if this map contains a mapping for the key */
+		public void remove(int key) {
+			this.values[new Integer(key).hashCode() % LEN] = -1;
+		}
+	}
+	``