509. 斐波那契数

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