Two-Pass

Intuition My thought was first going left to right checking both neighbours. For example, for [1,2,3,4] would work perfectly. However it’s not possible to solve this in one pass checking both neighbours. We need to use a two pass approach, LTR, RTL. To visualize better the problem, using [1,2,3,4] let’s see how many candies LTR and RTL would give for each children: LTR [1,2,3,4] -> [1,2,3,4] since it's always increase each children get's one more candy than the previous one. RTL [1,2,3,4] -> [1,1,1,1] From RTL perspective, it's always decreasing, so all children get's one. In this case the correct solution is [1,2,3,4] ...

Intuition This problem uses a very similar solution to 135. Candy. Important point to notice is: water can’t be at the edges, the edge is either 0 heigh (water leak) or wall with no water on top. So with this in mind we can ignore water on edges. The volume of water in any place is water = max_height - current_height. Let’s take this example [0,2,0,3,0,2], the # represents the walls, the . represents the water. ...