70. Climbing Stairs

• Difficulty: Easy

• Topics: Dynamic Programming

• Similar Questions:

  • Min Cost Climbing Stairs

  • Fibonacci Number

  • N-th Tribonacci Number

Problem:

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

Solutions:

class Solution {
public:
    int climbStairs(int n) {
        int prev = 0;
        int ret = 1;

        for (int i = 1; i <= n; ++i) {
            int temp = ret;
            ret = ret + prev;
            prev = temp;
        }

        return ret;

    }
};