[LEET-0000] add problem descriptions

Author: fishercoder1534

leetcode-algorithms/src/main/java/com/stevesun/solutions/BinaryTreeLevelOrderTraversal.java

@@ -29,7 +29,6 @@
 ]
 */
 public class BinaryTreeLevelOrderTraversal {
-	//Cheers, easily made it AC'ed on the first submission now, practice does make perfect!
 	public List<List<Integer>> levelOrder(TreeNode root) {
 		List<List<Integer>> result = new ArrayList<List<Integer>>();
 		if(root == null) return result;

leetcode-algorithms/src/main/java/com/stevesun/solutions/BinaryTreePostOrderTraversal.java

@@ -22,7 +22,7 @@
  Note: Recursive solution is trivial, could you do it iteratively?*/
 
 public class BinaryTreePostOrderTraversal {
-	/**modify the code for pre-order traversal so that it becomes root->right->left, and then reverse the result to get left->right->root, so tricky!!!*/
+	/**A tricky one: Modify the code for pre-order traversal so that it becomes root->right->left, and then reverse the result to get left->right->root.*/
     public static List<Integer> postorderTraversal_iterative(TreeNode root) {
         List<Integer> result = new ArrayList();
         Stack<TreeNode> stack = new Stack();

leetcode-algorithms/src/main/java/com/stevesun/solutions/CountUnivalueSubtrees.java

@@ -2,6 +2,20 @@
 
 import com.stevesun.common.classes.TreeNode;
 
+/**Given a binary tree, count the number of uni-value subtrees.
+
+ A Uni-value subtree means all nodes of the subtree have the same value.
+
+ For example:
+ Given binary tree,
+     5
+    / \
+   1   5
+  / \   \
+ 5  5   5
+ return 4.
+
+ */
 public class CountUnivalueSubtrees {
 
     public int countUnivalSubtrees(TreeNode root) {

leetcode-algorithms/src/main/java/com/stevesun/solutions/TwoSumIIInputArrayIsSorted.java

@@ -2,6 +2,17 @@
 
 import com.stevesun.common.utils.CommonUtils;
 
+/**
+ * Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.
+
+ The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.
+
+ You may assume that each input would have exactly one solution.
+
+ Input: numbers={2, 7, 11, 15}, target=9
+ Output: index1=1, index2=2
+
+ */
 public class TwoSumIIInputArrayIsSorted {
     public static int[] twoSum(int[] numbers, int target) {
         int left = 0, right = numbers.length-1;