746. 使用最小花费爬楼梯

• java

dp动态规划

class Solution {
   
    public int minCostClimbingStairs(int[] cost) {
   
        int n = cost.length;
        int[] d = new int[n + 1];
        d[0] = d[1] = 0;
        for (int i = 2; i < n + 1; ++i) {
   
            d[i] = Math.min(d[i - 1] + cost[i - 1], d[i - 2] + cost[i - 2]);
        }
        return d[n]; 
    }
}

使用滚动数组将空间复杂度从O(n)降到O(1)

class Solution {
   
    public int minCostClimbingStairs(int[] cost) {
   
        int n = cost.length;
        int pre = 0, cur = 0;
        for (int i = 2; i < n + 1; ++i) {
   
            int next = Math.min(cur + cost[i - 1], pre + cost[i - 2]);
            pre = cur;
            cur = next;
        }
        return cur; 
    }
}

注意数组的长度用.length获取
String的长度用.length()获取