[Leetcode Solution] Flatten Binary Tree to Linked List

Analysis

• A recursive out-of-place algorithm comes out
• A grace in-place algorithm can be found here

Note

• Define a return type as reference, then the return value could be used as a left-value
• In most case the recursion method may not be a in-place algorithm because the depth of recursion is usually in proportion to the input size. Thus the space used in store the stack is not constant

Code