- find the distance
- none of the distance is 0, two unique distances

```
def validSquare(self, p1, p2, p3, p4):
dist = []
ps = [p1, p2, p3, p4]
for i in range(4):
for j in range(i+1, 4, 1):
dist.append((ps[i][0] - ps[j][0])**2 + (ps[i][1] - ps[j][1])**2)
return len(set(dist)) == 2 and all(x != 0 for x in dist)
```