NP-complete problems aren't impossible, they just get very computationally expensive the bigger they get.

OP would only be rich & famous if they had developed an algorithm that solved minesweeper in polynomial or better time. (i.e., a time complexity on the order of O(n^k), where k is some constant)

Many NP-Complete problems are trivially solvable, just not trivially solvable in an efficient manner. - like the Travelling Salesman Problem. You can just try every possible combination. It's not fast, but it works.

Exactly what Yen said. People generally say "solve" to some sizes of the problem,. Obviously it isn't hard to solve a 4x4 minsweeper... maybe I need to rephrase: "I wrote a minesweeper game..."