70. Climbing Stairs

70. Climbing Stairs

由于每次只能迈1步或者两步台阶

拆解：

1. 起始状态
   1. nums[0] = 1、nums[1] = 1
2. 状态转移方程
   1. nums[i] = nums[i-1] + nums[i-2]

当然还可以优化：

public int climbStairs(int n) {
    if(n == 0 || n == 1) {
        return 1;
    }
    int prev = 1;
    int cur = 1;
    for (int i = 2; i <= n; i++) {
        int tmp = cur;
        cur = cur + prev;
        prev = tmp;
    }
    return cur;
}