TODO:

• test cases for SPOJ/FAMILY
• LISTREE
• ONEXLIS
• LIS2
• PRJAN15E
• MTOTALF
• FASTFLOW
• sliding windows: KPMATRIX, MATRIX2

Best practices: use method with following signature to easy switch between online, offline input mode void solve(istream& cin, ostream& cout);

Problems to revise: SPOJ/RHOMBS solution is very easy. but idea should be explained. there are probably some geometrical rules involved. SPOJ/MATCHING Hopcroft-Karp should be learnt and put into Ant library.

MxN plane 2D. height + elevation map. How much water can be trapped:
M,N < 110, 0 < h < 20'000. 

Sample:
[1,4,3,1,3,2]
[3,2,1,3,2,4] => 4
[2,3,3,2,3,1]

• pick any element of the grid, if has lower height - go there
• if has of equal height
• if greater, we do union find algo here such set has height at which it spills, also current level