【LeetCode】70

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? 

Hide Tags: Dynamic Programming

 

Solution:一个台阶的方法次数为1次，两个台阶的方法次数为2个。n个台阶的方法可以理解成上n-2个台阶，然后2步直接上最后一步；或者上n-1个台阶，再单独上一步

 

int climbStairs(int n) {    //Runtime:0ms
    int a=1,b=2;
    if(n==1)return a;
    if(n==2)return b;
    int c=0;
    for(int i=3;i<=n;i++){
        c=a+b;
        a=b;
        b=c;
    }
    return c;
}
int climbStairs2(int n){    ////Runtime:0ms
    if(n <= 2)return n;
    int* step = new int[n];  
    step[0] = 1;  
    step[1] = 2;  
    for(int i = 2; i < n; i++)step[i] = step[i-1] + step[i-2];  
    return step[n-1];  
}