leetcode/Alog_DP/509+Fibonacci Number.cpp at master · duanyaqi/leetcode · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
class Solution {
public:
    int fib(int n) {
        if (n <= 1) return n;
        vector<int> dp(n+1);
        dp[0] = 0;
        dp[1] = 1;

        for (int i = 2; i <= n; ++i) {
            dp[i] = dp[i-1] + dp[i-2];
        }

        return dp[n];
    }
};


class Solution {
public:
    int fib(int n) {
        if (n <= 1) return n;
        vector<int> dp(3);
        dp[0] = 0;
        dp[1] = 1;

        for (int i = 2; i <= n; ++i) {
            dp[2] = dp[0] + dp[1];
            dp[0] = dp[1];
            dp[1] = dp[2];
        }

        return dp[2];
    }
};

//best array cost less space than vector
class Solution {
public:
    int fib(int n) {
        if (n <= 1) return n;
        int dp[3];
        dp[0] = 0;
        dp[1] = 1;

        for (int i = 2; i <= n; ++i) {
            dp[2] = dp[0] + dp[1];
            dp[0] = dp[1];
            dp[1] = dp[2];
        }

        return dp[2];
    }
};