257. Binary Tree Paths

Check out the problem description here.

Binary Tree Paths - LeetCode

class Solution:
    def binaryTreePaths(self, root: Optional[TreeNode]) -> List[str]:
        res=[]
        ds=[]
        
        self.rec(root,res,ds)
        for i in range(len(res)):
            res[i] = "->".join(res[i])
        return(res)    
           
    def rec(self,root,res,ds):
        if root ==None:
            return
        ds.append(str(root.val))
        
        if root.left ==None and root.right==None:
            res.append(ds.copy())
            ds.pop(-1)
            return
        self.rec(root.left,res,ds)
        self.rec(root.right,res,ds)
        ds.pop(-1)

The above code in a much more neat code is given below

class Solution:
    def binaryTreePaths(self, root: Optional[TreeNode]) -> List[str]:
        res=[]
        if root:
            self.rec(root,"",res)
        return res
    
    def rec(self,root,path,res):

        if root == None :
            return
        path+=str(root.val)
        
        if root.right==None and root.left ==None:
            res.append(path)
            return
        
        self.rec(root.left,path+"->",res)
      
        self.rec(root.right,path+"->",res)

Both solution takes the same time and complexity

TIME :O(n) n= number of nodes

SPACE :O(h) h = height of the tree