【LeetCode】面試題 08.01. 三步問題

代碼

class Solution {
public:
	const int mod = 1e9 + 7;
	int waysToStep(int n) {
		vector<int> dp(n+4);
		dp[0] = 0;
		dp[1] = 1;
		dp[2] = 2;
		dp[3] = 4;
		for (int i=4;i<=n;i++)
		{
			dp[i] = ((dp[i - 1] % mod  + dp[i - 2] % mod ) % mod + dp[i - 3] % mod )%mod;
		}
		return dp[n];
	}
};