LeetCode——70. Climbing Stairs

70. Climbing Stairs
You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

Note: Given n will be a positive integer.

Example 1:

Input: 2
Output: 2
Explanation: There are two ways to climb to the top.

1. 1 step + 1 step
2. 2 steps

Example 2:

Input: 3
Output: 3
Explanation: There are three ways to climb to the top.

1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step

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解题思路
这道题也是简单的动态规划问题，思路和746. Min Cost Climbing Stairs一致。
注意使用数组的时候，要小心size为0或1时的特殊情况，提交使会提示如下：

//*** Error in `sandbox run': double free or corruption (out): 0x000000000104de70 ***

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代码如下：

class Solution {
public:
    int climbStairs(int n) {
        vector<int> ways(n, 0);
        if(n == 1) {
            return 1;
        }
        if(n == 2) {
            return 2;
        }
        ways[n-1] = 1;
        ways[n-2] = 2;
        for(int i = n - 3; i >= 0; i--) {
            ways[i] = ways[i+1] + ways[i+2];
        }
        return ways[0];
    }
    
};