Trapping Rain Waterhard

/**
 * @param {number[]} height
 * @return {number}
 */
function trap(height) {
    // TODO: two-pointer approach
    return 0;
}

console.log(trap([0,1,0,2,1,0,1,3,2,1,2,1])); // 6
console.log(trap([4,2,0,3,2,5]));               // 9