alg2025/src/8/12/trapping-rain-water.cpp

#include <vector>
using namespace std;

class Solution {
public:
    int trap(std::vector<int> &height) {

        if (height.size() < 3) {
            return 0;
        }
        int n = height.size();
        int l = 0, r = n - 1;

        int lmax = 0;
        int rmax = 0;

        long long totw = 0;
        while (l < r) {
            lmax = std::max(lmax, height[l]);
            rmax = std::max(rmax, height[r]);
            if (lmax < rmax) {
                totw += lmax - height[l];
                l++;
            } else {
                totw += rmax - height[r];
                r--;
            }
        }
        return totw;
    }
};

int main() {
}