斐波那契数列计算方法怎么使用

var memory = {};

function fib(n){

    if (n<=2) {

        return 1;

    } 

    if (memory[n]) {

        return memory[n];

    }

    return memory[n] = fib(n-1) + fib(n-2);

}



function fibnocache(n){

    if (n<=2) {

        return 1;

    } 

    return (fibnocache(n-1) + fibnocache(n-2));

}





function fib2(n) {

    if (n <= 1) {

        return n;

    }

    var prev = 0, current = 1;

    var tmp;

    for (var i = 1; i < n; i++) {

        tmp = current + prev;

        prev = current;

        current = tmp;

    }

    return current;

}



console.time('fib')

fib(40);

console.timeEnd('fib')

console.time('fibnocache')

fibnocache(40);

console.timeEnd('fibnocache')

console.time('fib2')

fib2(40);

console.timeEnd('fib2')