[leetcode]-70. Climbing Stairs（C语言）

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

int climbStairs(int n) {
    if(n==1)
        return 1;
    int first=1;
    int second=2;
    int i;
    int third;
    for(i=3;i<=n;i++)
    {
        third=first+second;
        first=second;
        second=third;
    }
    return second;
}