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Author: Chris Wu

problems/binary-tree-paths.py

@@ -0,0 +1,18 @@
+class Solution(object):
+    def binaryTreePaths(self, root):
+        if not root: return []
+        
+        arrow = '->'
+
+        ans = []
+        stack = []
+        stack.append((root, ''))
+
+        while stack:
+            node, path = stack.pop()
+            path += arrow+str(node.val) if path else str(node.val) #add arrow except beginnings
+            if not node.left and not node.right: ans.append(path) #if isLeaf, append path.
+            if node.left: stack.append((node.left, path))
+            if node.right: stack.append((node.right, path))
+
+        return ans

problems/longest-univalue-path.py

@@ -0,0 +1,23 @@
+class Solution(object):
+    def longestUnivaluePath(self, root):
+        def getUnivalueLength(node, val):
+            if not node: return 0
+            
+            l, r = getUnivalueLength(node.left, node.val), getUnivalueLength(node.right, node.val)
+            self.ans = max(self.ans, l+r)
+            
+            if node.val==val: return 1+max(l, r)
+            return 0
+            
+        if not root: return 0
+        self.ans = float('-inf')
+        getUnivalueLength(root, root.val)
+        return self.ans
+
+"""
+The main I idea is simple.
+Traverse all the node.
+Each node, we assume that the longestUnivaluePath will pass through it.
+So we can update the `self.ans` if `l+r` is larger.
+At the same time, `getUnivalueLength()` will return the max length of the path (start from itself) which has the value `val`.
+"""