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leetcode 70. Climbing Stairs (DP)

2020/8/20 10:32:40   来源:

文章目录

      • C++
      • Java
      • Python
      • Go

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?

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

Constraints:

1 <= n <= 45

  • 动态规划

C++

class Solution {
public:
    int climbStairs(int n) {
        if(n<=2)return n;
        int f=1,g=2;
        for(int i=2;i<n;i++){
            int tmp=g;
            g=f+g;
            f=tmp;
        }
        return g;
    }
};

Java

class Solution {
    public int climbStairs(int n) {
        if(n<=2)return n;
        int f=1;
        int g=2;
        for(int i=2;i<n;i++){
            int tmp=g;
            g=f+g;
            f=tmp;
        }
        return g;
    }
}

Python

class Solution:
    def climbStairs(self, n: int) -> int:
        if n<=2:
            return n
        f,g=1,2
        for i in range(2,n):
            f,g=g,f+g
        return g

Go

func climbStairs(n int) int {
    if n<=2 {
        return n
    }
    f,g:=1,2
    for i:=2;i<n;i++ {
        f,g=g,f+g
    }
    return g
}