TrappingRainWater.py ( using 2 pointers )

class Solution:
    def trap(self, height: List[int]) -> int:
         # Initialize two pointers: L for the leftmost position, R for the rightmost
        L, R = 0, len(height) - 1
        # Track the maximum height on the left and right sides of the current position
        leftMax, rightMax = height[L], height[R]
        # Variable to get the total volume of water trapped
        res = 0
        # Continue until L meets R
        while L < R:
        # If the height on the left side is shorter, move L to the right
            if leftMax < rightMax:
                L+=1
                # Update leftMax with the maximum height encountered so far on the left
                leftMax = max(leftMax, height[L])
                # Add difference between leftMax and the current height at L to the result
                res += leftMax - height[L]
            else:
                # Otherwise, move R to the left
                R-=1
                # Update rightMax with the maximum height encountered so far on the right
                rightMax = max(rightMax, height[R])
                # Add difference b/w rightMax and the current height at R to the result
                res += rightMax - height[R]
        # Return the total volume of water trapped
        return res