javascript 求最大前5个数; 对象 深拷贝 deep copy

* 用数组

function getTopN(a, n) {

	function _cloneArray(aa) {
    	var n = aa.length, a = new Array(n);
    	for (var i = 0; i < n; i++) {
    		a[i] = aa[i];
    	}
    	return a;
    }

    function _getMaxElem(a) {    	
        if (a.length === 0)
        	throw "empty array"; 

        if (a.length === 1)
            return { index: 0, value: a[0] };        

        var max = a[0],
            index = 0;
        for (var i = 0; i < a.length; i++) {
            if (a[i] > max) {
                max = a[i];
                index = i;
            }
        }
        return {
            index: index,
            value: max
        }
    }

    var o = {}, b = [], c = _cloneArray(a);;
    while (n--) {
        o = _getMaxElem(c);
        b.push(o.value);
        c.splice(o.index, 1);
    }

    return b;
}

 // test

 

/*
var a= [];
for (var i = 0; i < 12; i++) {
    a.push(Math.round(Math.random()*100));
}
console.log(a);
*/

var a = [3, 12, 17, 16, 73, 32, 61, 46, 52, 49, 6, 5];
var b = getTopN(a, 5);
console.log('max elements: [' + b.toString() + ']');  // [73,61,52,49,46]

console.log('-------------sorted------------------');
console.log(a.sort(function(a, b) { return b - a; }));

 

 

* 用链表 []

  + splice方法    点击查看我自己的博客 https://www.cnblogs.com/mingzhanghui/p/9317179.html

 

function getTopN(a, n) {

    function _getMaxElem(a) {
        if (a.length === 0)
            throw "empty array";

        if (a.length === 1)
            return { index: 0, value: a[0] };

        var max = a.get(0), index = 0, c;
        for (var i = 0; i < a.length; i++) {
            c = a.get(i);
            if (c > max) {
                max = c;
                index = i;
            }
        }
        return {
            index: index,
            value: max
        }
    }

    var o = {}, b = [];
    while (n--) {
        o = _getMaxElem(a);
        b.push(o.value);
        a.splice(o.index, 1);
    }

    return b;
}

/**
 * max elements: [73,61,52,49,46]
 * -------------sorted------------------
 * [ 73, 61, 52, 49, 46, 32, 17, 16, 12, 6, 5, 3 ]
 */
var a = [3, 12, 17, 16, 73, 32, 61, 46, 52, 49, 6, 5];
var list = new LinkedList(a);
var top5 = getTopN(list, 5);
console.log('max elements: [' + top5.toString() + ']');
console.log('-------------sorted------------------');
console.log(a.sort(function(a, b) { return b - a; }));

　　

-------------------------------------------------------------------

clone object:

 

function clone(obj) {
    // Handle the 3 simple types, and null or undefined
    if (null == obj || "object" != typeof obj) return obj;
    var copy;

    // Handle Date
    if (obj instanceof Date) {
        copy = new Date();
        copy.setTime(obj.getTime());
        return copy;
    }

    // Handle Array
    if (obj instanceof Array) {    
    	var n = obj.length;
    	copy = new Array(n);
    	for (var i = 0; i < n; i++) {
    		copy[i] = obj[i];
    	}
    	return copy;
    }

    // Handle Object
    if (obj instanceof Object) {
        copy = {};
        for (var attr in obj) {
            if (obj.hasOwnProperty(attr)) {
            	copy[attr] = clone(obj[attr]); // 双向循环列表会无限递归🤔 stackoverflow 
            }
        }
        return copy;
    }

    throw new Error("Unsupported type for copying object...");
}

 

// test:

 

// test
var o = { name1:[1,2,3,4], name2:{ inner1:[1,2], inner2: null, inner3:{a:[1,2], b:"this is good", c:3, d:null, e:undefined}} };
var p = clone(o);
console.log(o===p);   // false
console.log(o.toString()===p.toString()); // true

console.log('----------');

var date1 = new Date();
var date2 = clone(date1);
var date3 = date1;
console.log(date2===date1);  // false;
console.log(date2.getTime()===date1.getTime());  // true
console.log(date3===date1);   // true;