42-Trapping-Rain-Water.cpp

class Solution {
public:
    int trap(vector<int>& height) {
    if (height.empty()) {
        return 0;
    }
    
    int left = 0, right = height.size() - 1;
    int left_max = 0, right_max = 0;
    int total_water = 0;
    
    while (left <= right) {
        if (height[left] <= height[right]) {
            if (height[left] >= left_max) {
                left_max = height[left];
            } else {
                total_water += left_max - height[left];
            }
            left++;
        } else {
            if (height[right] >= right_max) {
                right_max = height[right];
            } else {
                total_water += right_max - height[right];
            }
            right--;
        }
    }
    
    return total_water;
}

};