#2158 - Amount of New Area Painted Each Day

Problem Description

There is a long and thin painting that can be represented by a number line. You are given a 0-indexed 2D integer array paint of length n, where paint[i] = [starti, endi]. This means that on the ith day you need to paint the area between starti and endi.

Painting the same area multiple times will create an uneven painting so you only want to paint each area of the painting at most once.

Return an integer array worklog of length n, where worklog[i] is the amount of new area that you painted on the ith day.

Solution

/**
 * @param {number[][]} paint
 * @return {number[]}
 */
var amountPainted = function(paint) {
  const intervals = new Map();
  const result = [];

  for (const [start, end] of paint) {
    let left = start;
    let right = end;
    let paintAmount = right - left;

    const keys = Array.from(intervals.keys()).sort((a, b) => a - b);
    const toRemove = [];
    let merged = false;

    for (const key of keys) {
      const value = intervals.get(key);

      if (key > right || value < left) continue;

      if (!merged && key <= left && value >= left) {
        left = Math.min(left, key);
        right = Math.max(right, value);
        paintAmount = Math.max(0, end - Math.max(start, value));
        toRemove.push(key);
        merged = true;
      } else if (key >= left && key < right) {
        paintAmount -= Math.min(right, value) - key;
        right = Math.max(right, value);
        toRemove.push(key);
      } else if (value > left && value <= right) {
        paintAmount -= value - Math.max(left, key);
        left = Math.min(left, key);
        toRemove.push(key);
      }
    }

    for (const key of toRemove) {
      intervals.delete(key);
    }

    intervals.set(left, right);
    result.push(Math.max(0, paintAmount));
  }

  return result;
};