题目:
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
AC:
class Solution {
public int climbStairs(int n) {
if (n <= 3) {
return n;
}
int first = 2;
int second = 3;
int third = first + second;
for (int i = 4; i <= n; i++) {
third = first + second;
first = second;
second = third;
}
return third;
}
}