0070. Climbing Stairs.md

Climbing Stairs, easy

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

// 0ms
class Solution {
public:
    int climbStairs(int n) {
        if (n < 2) return 1;

        vector<int> v(n+1, 0);
        v[0] = 0;
        v[1] = 1;
        v[2] = 2;
        for (int i = 3; i <= n; i++) {
            v[i] = v[i-1] + v[i-2];
        }
        return v[n];
    }
};

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