Fibonacci C语言实现

long long int Fibonacci(int n)
{
    int i;
    long long int *dp, ret;
    dp = malloc(sizeof(long long int ) * (n+1));
    
    dp[0]=0; dp[1] = 1; 
    for (i=2; i<= n; i++) {
        dp[i] = dp[i-1] + dp[i-2];
    }
    ret = dp[n];
    free(dp);
    return ret;
}

上面就是之前写的代码,看上去能够解决问题,但是今天看了https://www.cnblogs.com/MonsterJ/p/13154306.html 的分析,感觉自己弱爆了,连时间复杂度都没分析.

直接上时间更优化的代码:

 int fib(int N) {
        if (N == 0) {
            return 0;
        }
        if (N== 1) {
            return 1;
        }
        int *notes = malloc(sizeof(int) * (N+1));
        if (notes == NULL) 
            return -1;
        
        notes[0] = 0;
        notes[1] = 1;
       int i;
        for( i = 2; i <= N; i++) {
            notes[i] = notes[i-1] + notes[i-2];
        }
        int res = notes[N];
        free(notes);
        return  res;
    }

再上空间上更简化的代码:

 int fib(int N) {
        int a = 0;
        int b = 1;
        if(N == 0) {
            return a;
        }
        if(N == 1) {
            return b;
        }
        for(int i = 2; i <= N; i++) {
            int tmp = a + b;
            a = b;
            b = tmp;
        }
        return b;
    }