使用循环

class Solution {public int fib(int n) {if(n == 0){return 0;}if(n == 1){return 1;}int res = 0;int pre1 = 1;int pre2 = 0;for(int i = 2; i <= n; i++){res = pre1 + pre2;pre2 = pre1;pre1 = res;}return res;}
}

使用HashMap

class Solution {private Map<Integer,Integer> storeMap = new HashMap();public int fib(int n) {if(n == 0){return 0;}if(n == 1){return 1;}if(null != storeMap.get(n)){return storeMap.get(n);}else{int res = fib(n-1) + fib(n-2);storeMap.put(n,res);return res;}}
}