I was asked the below question in my Google phone interview.

Problem: given a list of leaf nodes in a pyramid ，and a map which indicates what's the possible parent node given a left and right node. Return true if the one of leaf node could turn into the root node, Otherwise, return false.

```
Example:
root
/ \
X X
/\ /\
X X X
/ \/ \/ \
A B C D
Map:
left: A | B | C | D
right ---------------------------------
A B | A or C | D | A
B D |B or C | A |
C B
D
```

Note:1. If left child is B, right child is A, the parent node could be B or C

Refer: https://stackoverflow.com/questions/43432699/string-pyramid-transition-matrix