I am unable to understand the ICPC problem’s solution Problem.

I do not understand that how this came up (how this striked? and how does it leads us to number of integral points!)

```
Dx = (x2 - x1)
Dy = (y2 - y1)
x = x1 + Dx * t
y = y1 + Dy * t
```

Please help me!! Why have we written it like this , it is quite non striking for me ! Morover,the next statements are unclear. I just need to know how to calculate the number of Integral points through which the line segment passes.