paint-house.js

/**
 * Paint House
 *
 * There are a row of n houses, each house can be painted with one of the three colors: red, blue or green. The cost of
 * painting each house with a certain color is different. You have to paint all the houses such that no two adjacent
 * houses have the same color.
 *
 * The cost of painting each house with a certain color is represented by a n x 3 cost matrix. For example, costs[0][0]
 * is the cost of painting house 0 with color red; costs[1][2] is the cost of painting house 1 with color green, and so
 * on...
 *
 * Find the minimum cost to paint all houses.
 *
 * Note:
 * All costs are positive integers.
 *
 * Example:
 *
 * Input: [[17,2,17],[16,16,5],[14,3,19]]
 * Output: 10
 * Explanation: Paint house 0 into blue, paint house 1 into green, paint house 2 into blue.
 *              Minimum cost: 2 + 5 + 3 = 10.
 */

/**
 * @param {number[][]} costs
 * @return {number}
 */
const minCost = costs => {
  if (!costs || costs.length === 0) {
    return 0;
  }

  const n = costs.length; // n houses

  // costs[i]]j] represents the minimum cost of painting house i with color j
  for (let i = 1; i < n; i++) {
    costs[i][0] += Math.min(costs[i - 1][1], costs[i - 1][2]);
    costs[i][1] += Math.min(costs[i - 1][0], costs[i - 1][2]);
    costs[i][2] += Math.min(costs[i - 1][1], costs[i - 1][0]);
  }

  return Math.min(Math.min(costs[n - 1][0], costs[n - 1][1]), costs[n - 1][2]);
};

export { minCost };