packagemedium;

importclasses.TreeNode;

publicclassCountUnivalueSubtrees {

publicintcountUnivalSubtrees(TreeNoderoot) {

int[]count =newint[1];

helper(root,count);

returncount[0];

}

privatebooleanhelper(TreeNodenode,int[]count) {

if (node ==null) {

returntrue;

}

booleanleft =helper(node.left,count);

booleanright =helper(node.right,count);

if (left &&right) {

if (node.left !=null &&node.val !=node.left.val) {

returnfalse;

}

if (node.right !=null &&node.val !=node.right.val) {

returnfalse;

}

count[0]++;

returntrue;

}

returnfalse;

}

}

|259|[3Sum Smaller](https://leetcode.com/problems/3sum-smaller/)|[Solution](../../blob/master/MEDIUM/src/medium/_3Sum_Smaller.java)| O(n^2)|O(1)| Medium|

|257|[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)|[Solution](../../blob/master/EASY/src/easy/BinaryTreePaths.java) | O(n*h) | O(h) | DFS/Recursion

|252|[Meeting Rooms](https://leetcode.com/problems/meeting-rooms/)|[Solution](../../blob/master/EASY/src/easy/MeetingRooms.java)| O(nlogn)| O(1)|

|250|[Count Univalue Subtrees](https://leetcode.com/problems/count-univalue-subtrees/)|[Solution](../../blob/master/MEDIUM/src/medium/CountUnivalueSubtrees.java)| O(n)|O(h) | Medium| DFS

|249|[Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings/)|[Solution](../../blob/master/EASY/src/easy/GroupShiftedStrings.java)| O(nlogn)| O(n)|

|246|[Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/)|[Solution](../../blob/master/EASY/src/easy/StrobogrammaticNumber.java)| O(n)| O(1)|

|243|[Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/)|[Solution](../../blob/master/EASY/src/easy/ShortestWordDistance.java)| O(n)| O(1)|