Min Cost Climbing Stairs

1function minCostClimbingStairs(cost) {2  const memo = new Map();3  const reach = (i) => {                         // cheapest way to arrive at step i4    if (i <= 1) return 0;                        // you may start on step 0 or 15    if (memo.has(i)) return memo.get(i);6    const best = Math.min(reach(i - 1) + cost[i - 1], reach(i - 2) + cost[i - 2]);7    memo.set(i, best);8    return best;9  };10  return reach(cost.length);                     // the top is past the last step11}

1function minCostClimbingStairs(cost) {2  const n = cost.length;3  const reach = new Array(n + 1).fill(0);        // reach[0] = reach[1] = 0: start for free4  for (let i = 2; i <= n; i++) {5    reach[i] = Math.min(reach[i - 1] + cost[i - 1],   // from one step below6                        reach[i - 2] + cost[i - 2]);  // or from two below7  }8  return reach[n];                               // the top9}

1function minCostClimbingStairs(cost) {2  let twoBelow = 0, oneBelow = 0;                // reach[i - 2], reach[i - 1]3  for (let i = 2; i <= cost.length; i++) {4    [twoBelow, oneBelow] = [oneBelow, Math.min(oneBelow + cost[i - 1], twoBelow + cost[i - 2])];5  }6  return oneBelow;7}