Sunday, April 5, 2015

LeetCode [70] Climbing Stairs

 70. Climbing Stairs

Easy

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
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//C++
//C++: 0ms
class Solution {
public:
    int climbStairs(int n) {
        if(n<=2) return n;
        vector<int> dp(n, 0);
        dp[0] = 1;
        dp[1] = 2;
        for(int i=2; i<n; ++i){
            dp[i] = dp[i-2]+dp[i-1];
        }
        return dp[n-1];
    }
};

//Java
class Solution {
    public int climbStairs(int n) {
        int[] dp = new int[n+1];
        dp[0] = 1;
        dp[1] = 1;
        for(int i=2; i<=n; ++i){
            dp[i] = dp[i-1]+dp[i-2];
        }
        return dp[n];
    }
}

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