LeetCode in Erlang

11. Container With Most Water

Medium

Given n non-negative integers a1, a2, ..., an , where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of the line i is at (i, ai) and (i, 0). Find two lines, which, together with the x-axis forms a container, such that the container contains the most water.

Notice that you may not slant the container.

Example 1:

Input: height = [1,8,6,2,5,4,8,3,7]

Output: 49

Explanation: The above vertical lines are represented by array [1,8,6,2,5,4,8,3,7]. In this case, the max area of water (blue section) the container can contain is 49.

Example 2:

Input: height = [1,1]

Output: 1

Example 3:

Input: height = [4,3,2,1,4]

Output: 16

Example 4:

Input: height = [1,2,1]

Output: 2

Constraints:

• n == height.length
• 2 <= n <= 105
• 0 <= height[i] <= 104

Solution

-spec max_area([integer()]) -> integer().
max_area(Height) ->
    TupleHeight = list_to_tuple(Height),
    max_area(TupleHeight, 0, length(Height) - 1, 0).

max_area(_, Left, Right, MaxArea) when Left >= Right ->
    MaxArea;
max_area(TupleHeight, Left, Right, MaxArea) ->
    LeftHeight = element(Left + 1, TupleHeight),
    RightHeight = element(Right + 1, TupleHeight),
    Width = Right - Left,
    CurrentArea = min(LeftHeight, RightHeight) * Width,
    NewMaxArea = max(MaxArea, CurrentArea),
    
    % Move the pointer pointing to the shorter line
    case LeftHeight < RightHeight of
        true  -> max_area(TupleHeight, Left + 1, Right, NewMaxArea);
        false -> max_area(TupleHeight, Left, Right - 1, NewMaxArea)
    end.

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