113. Path Sum II（求等于某个数的所有路径）

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / 
            4   8
           /   / 
          11  13  4
         /      / 
        7    2  5   1

return

[
   [5,4,11,2],
   [5,8,4,5]
]

class Solution {
    List<List<Integer>> res = new ArrayList<>();
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<Integer> curres = new ArrayList<Integer>();
        help(root,0,sum,curres);
        return res;
    }
    private void  help(TreeNode root,int sum ,int target,List<Integer> curres){
        if(root == null) return ;
        curres.add(root.val);
        if(root.left==null && root.right==null && sum+root.val==target) 
            res.add(new ArrayList(curres));
        help(root.left,sum+root.val,target,curres);
        help(root.right,sum+root.val,target,curres);
        curres.remove(curres.size()-1);
    }
}