leetcode70—Climbing Stairs

Posted 2021-01-20 tingweichen

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

想法：动态规划分解成子问题，到达n之前，走1步或者2步。即可表示成result[n]=result[n-1]+result[n-2]

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