题目链接:https://leetcode-cn.com/problems/three-steps-problem-lcci/
题目如下:
class Solution { public: int waysToStep(int n) { if(n==1) return 1; if(n==2) return 2; if(n==3) return 4; #define MOD 1000000007 long long dp[n+1]; dp[1]=1;dp[2]=2;dp[3]=4; for(int i=4;i<n+1;i++){ dp[i]=(dp[i-1]+dp[i-2]+dp[i-3])%MOD; } return dp[n]; } };