Leetcode 70 Climbing Stairs

dp[i] means the minimum cost to reach i-th (index start from 0) stair.

DP formula:

dp[i] = min(dp[i-1], dp[i-2])+cost[i]     i>=2

base cases: dp[0]=cost[0]; dp[1]=cost[1];

target: min(dp[n-1], dp[n-2])