[Leet Code - eazy] 70.String to Integer (atoi)

You are climbing a staircase. It takes n steps to reach the top.

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

 

Example 1:

Input: n = 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps

Example 2:

Input: n = 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

 

Constraints:

• 1 <= n <= 45

 

이해해야될 풀이

 

/**
 * @param {number} n
 * @return {number}
 */
var climbStairs = function(n) {

    if (n < 2) {

        return 1;
    }

        let firstStep = 1;

        let secondStep = 1;

        let thirdStep = 0;

        for (let i=2; i<=n; i++) {

            thirdStep = firstStep + secondStep;

            firstStep = secondStep;

            secondStep = thirdStep;
        }

        return thirdStep;
        
};