Given a binary tree, find the largest subtree which is a Binary Search Tree (BST), where largest means subtree with largest number of nodes in it.

Note:
A subtree must include all of its descendants.

Example:

Input: [10,5,15,1,8,null,7]

   10 
   / \ 
  5  15 
 / \   \ 
1   8   7

Output: 3
Explanation: The Largest BST Subtree in this case is the highlighted one.
             The return value is the subtree's size, which is 3.

public ListNode reverse(ListNode head){
	if(head==null)return null;
	ListNode pre=null;
	ListNode cur=head;
	while(cur!=null){
		ListNode next=cur.next;
		cur.next=pre;
		pre=cur;
		cur=next;
	}
	return pre;
}

string minWindow(string s, string t) {
        vector<int> map(128,0);
        for(auto c: t) map[c]++;
        int counter=t.size(), begin=0, end=0, d=INT_MAX, head=0;
        while(end<s.size()){
            if(map[s[end++]]-->0) counter--; //in t
            while(counter==0){ //valid
                if(end-begin<d)  d=end-(head=begin);
                if(map[s[begin++]]++==0) counter++;  //make it invalid
            }  
        }
        return d==INT_MAX? "":s.substr(head, d);
    }

Given a directed, acyclic graph of N nodes.  Find all possible paths from node 0 to node N-1, and return them in any order.

The graph is given as follows:  the nodes are 0, 1, ..., graph.length - 1.  graph[i] is a list of all nodes j for which the edge (i, j) exists.

Example:
Input: [[1,2], [3], [3], []] 
Output: [[0,1,3],[0,2,3]] 
Explanation: The graph looks like this:
0--->1
|    |
v    v
2--->3
There are two paths: 0 -> 1 -> 3 and 0 -> 2 -> 3.

Given a binary array, find the maximum length of a contiguous subarray with equal number of 0 and 1.

Given an integer matrix, find the length of the longest increasing path.

From each cell, you can either move to four directions: left, right, up or down. You may NOT move diagonally or move outside of the boundary (i.e. wrap-around is not allowed).