leetcode 斐波那契数列 javascript实现

/**
 * @param {number} n
 * @return {number}
 */
// 递归
 let arr = [0,1];
   var fib = function(n) {
     if(n<2){
         return n
    }
     if(arr[n]){
         return  arr[n]
   }
     arr[n]=(fib(n-1)+fib(n-2))%1000000007
     return arr[n]
 };


// 动态规划
var fib = function(n) {
    let arr = [0,1]
    for(let i=2; i<=n; i++){
        arr[i] = (arr[i-1] + arr[i-2])%1000000007
    }   
    return arr[n]
};


// 动态规划 + 滚动数组
var fib = function(n) {
    if(n<2){
        return n
    }
    let pre = 0;
    let cur = 1;
    for(let i=2; i<=n; i++){
        let sum = (pre + cur)%1000000007;
        pre=cur;
        cur=sum;
    }   
    return cur
};