JSFiddle - React, Tailwind, and code Playground

by Shedal

CSS

body {
    font-family: arial;
    font-size: 72px;
    font-weight: bold;
}

JavaScript

function calcVolume(land) {
    var r = land.length - 1, l = 0, rm = 0, lm = 0, v = 0;

    while(l < r) {
        lm = Math.max(land[l], lm);
        rm = Math.max(land[r], rm);

        v += (lm >= rm) ? (rm - land[r--]) : (lm - land[l++]);
    }

    return v;
}

var land = [2, 5, 1, 3, 1, 2, 1, 7, 7, 6];

document.body.innerHTML = calcVolume(land);