A brief discussion on loop vs recursion

For example, iterate through the following one-dimensional array:

Copy the codeThe code is as follows:

[javascript] view plaincopyprint?
var a1 = [1];  
var a2 = [1, 2];  
var a3 = [1, 2, 3];  

Although they vary in length, it is very easy to deal with them and elegantly:

Copy the codeThe code is as follows:

[javascript] view plaincopyprint?
var dumpArrayByLoop = function(a) {
    for (var i = 0; i < ; i++) {
        println(a[i]);
    }
};

If you use recursion instead, it will look awkward:

Copy the codeThe code is as follows:

[javascript] view plaincopyprint?
var dumpArrayByRecur = function(i, a) {
    if (i < ) {
        println(a[i]);
        dumpArrayByRecur(i + 1, a);
    }
};

They can output the same result, but by comparison, the recursive version looks clumsy.

Now think about it, if the metadata changes: the dimension expands to two-dimensional.

Copy the codeThe code is as follows:

[javascript] view plaincopyprint?
var a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

At this time, another layer of cycle needs to be installed outside to become a double cycle:

Copy the codeThe code is as follows:

[javascript] view plaincopyprint?
var dumpArrayByLoop = function(a) {  
    for (var i = 0; i < ; i++) {  
        for (var j = 0; j < a[i].length; j++) {  
            println(a[i][j]);  
        }  
    }  
};  

If the dimension of the data continues to expand, it will become a three-dimensional, four-dimensional, and even a dynamic N-dimensional array. How to deal with using loops?

In this case where the number of "layers" is very deep or even uncertain, it is necessary to use "recursion" to solve the problem across "layers".

Copy the codeThe code is as follows:

[javascript] view plaincopyprint?
var isArray = function(a) {
    return (a) === '[object Array]';
};

var dumpArrayByRecur = function(a) {
    if (isArray(a)) {
        for (var i = 0; i < ; i++) {
            dumpArray(a[i]);
        }
    } else {
        println(a);
    }
};

In the above code, if you find that the child node is an array, you use recursion to enter the next layer; while traversal on the same layer is completed using a loop.