Min Cost Climbing Stairs

Min Cost Climbing Stairs

You are given an integer array cost where cost[i] is the cost of the i-th step on a staircase. Once you pay the cost, you can either climb 1 or 2 steps.

You can either start from the step with index 0, or the step with index 1.

Return the minimum cost to reach the top of the floor.

The top of the floor is one step beyond the last step (i.e., index cost.length).

Examples

Example 1:

Input: cost = [10, 15, 20]
Output: 15
Explanation: You start at step 1 (cost 15), then climb 2 steps to reach the top.
Total cost: 15.

Example 2:

Input: cost = [1, 100, 1, 1, 1, 100, 1, 1, 100, 1]
Output: 6
Explanation: Start at step 0 and follow the cheapest path:
Step 0 (cost 1) -> Step 2 (cost 1) -> Step 3 (cost 1) -> Step 5 is expensive,
so Step 4 (cost 1) -> Step 6 (cost 1) -> Step 7 (cost 1) -> Top.
Total cost: 1 + 1 + 1 + 1 + 1 + 1 = 6.

Constraints

• 2 <= cost.length <= 1000
• 0 <= cost[i] <= 999

Expected Complexity

• Time: O(n)
• Space: O(1)