Rainwater

class Solution {
public:
    vector<int> l(vector<int>& height) {
        int n = height.size();
        vector<int> lm(n);
        lm[0] = height[0];
        for (int i = 1; i < n; ++i) {
            lm[i] = max(lm[i - 1], height[i]);
        }
        return lm;
    }

    vector<int> r(vector<int>& height) {
        int n = height.size();
        vector<int> rm(n);
        rm[n - 1] = height[n - 1];
        for (int i = n - 2; i >= 0; --i) {
            rm[i] = max(rm[i + 1], height[i]);
        }
        return rm;
    }

    int trap(vector<int>& height) {
        int n = height.size();
        if (n == 0) return 0;
        
        vector<int> lm = l(height);
        vector<int> rm = r(height);
        int totalWater = 0;

        for (int i = 0; i < n; ++i) {
            int waterLevel = min(lm[i], rm[i]);
            if (waterLevel > height[i]) {
                totalWater += waterLevel - height[i];
            }
        }

        return totalWater;
    }
};