project euler problem 081, 082, 083

Path sum: two ways, three ways, four ways

project euler problem 081, two ways
Very simple dynamic programming problem. Warm up for the next two problem.

project euler problem 082, three ways
A little bit more complicated. Still simple dynamic programming problem. warm up problem. 

project euler problem 083 four ways

This is a real problem.  Not that simple. I used the C++ STL priority_queue to solve this problem, fast  and simple.   16ms with my debug version.