class Solution {
public:
    int maxArea(vector<int>& heights) {
        if (heights.size() <= 1) return 0;
        int i = 0, j = heights.size(), max_vol = 0;  // accessing out of bound j should be size - 1
        while (i < j) {
            int curr = min(heights[i], heights[j]) * (j - i);
            max_vol = max(curr, max_vol);
            if (heights[i] < heights[j]) {
                i++;
            } else {
                j--;
            }
        }
        return max_vol;
    }
};