70. 爬楼梯 leetcode

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class Solution {
    func climbStairs(_ n: Int) -> Int {
        if n == 0||n == 1 {
            return n
        }
        var arr = [Int].init(repeating: 1, count: n + 1)
        arr[0] = 1
        arr[1] = 1
        for i in 2...n{
            arr[i] = arr[i - 1] + arr[i - 2];
        }
        return arr[n];
    }
}