Turn around the situation

The final step is to make our solution iterative. With the previous (top-down) solution, we started with n and then repeatedly broke it down into smaller and smaller values until we reached n == 0 and n == 1. Instead, we will start with the base case and work our way up.

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function fib(n) {

    if (n === 0) return 0;

​

    // initialize cache

    let cache = new Array(n + 1).fill(0);

    cache[1] = 1;

​

    // iteratively fill cache

    for (let i = 2; i <= n; i++) {

        cache[i] = cache[i - 1] + cache[i - 2];

    }

    return cache[n];

}

​

console.log(fib(5));