O(n) solution for "Water in a Bar Graph" Problem

// O(n) solution for "Water in a Bar Graph" Problem.
var bar = [10,2,10, 1, 3, 7];
var water = 0;
var maxIndex = 0;
for (var i = 1; i < bar.length - 1; i++) {
    if (bar[i] < bar[maxIndex]) {
    water += bar[maxIndex] - bar[i];
  } else {
    maxIndex = i;
  }
}
if (bar[bar.length - 1] < bar[maxIndex]) {
    water -= (bar.length - 2 - maxIndex) * Math.abs(bar[bar.length - 1] - bar[maxIndex]);
}

document.write(water);