Problems:
1. Build Order (Topological Sort)
`Given Input
{
'A': ['B', 'C'],
'B': ['D'],
'C' :[],
'D': ['H'],
'E': ['A', 'F'],
'F' :['I'],
'G': ['B'],
'H': [],
'I': []
}'
Expected Output (The Order can change if there are no dependencys to build)
// I -> H -> C -> D -> B -> G -> F -> A -> E
2. https://leetcode.com/problems/number-of-islands/
3. https://leetcode.com/problems/trapping-rain-water/
4. https://leetcode.com/problems/lru-cache/