leetcode解题方案--070--Climbing Stairs

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 step + 1 step

2 steps

Example 2:

Input: 3

Output: 3

Explanation: There are three ways to climb to the top.

1 step + 1 step + 1 step

1 step + 2 steps

2 steps + 1 step

分析

每一个n为n-2走2步和n-1走1步。所以每一个操作数都是前两个之和。

一定要考虑n<2情况

class Solution {
public static int climbStairs(int n) {
if (n == 0) {
return 0;
}

int last = 0;
int thi = 1;
for (int i = 0; i<=n; i++) {
int tmp = thi;
thi = thi+last;
last = tmp;
}
return last;
}
}