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Example codes for 3 types of merge operations in js_javascript skills

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Release: 2016-05-16 17:18:09
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第一种:

复制代码 代码如下:

/**Brother Liang's*/
function merge(a, b) {
    var aLen = a.length,
        bLen = b.length,
        maxLen = Math.max(aLen, bLen),
        sumLen = aLen bLen,
        result = [],
        ap = 0,
        bp = 0;

     while (result.length < sumLen) {
        if (ap < aLen && bp < bLen) {
            if(a[ap] > b[bp]){
                result.push(b[bp ]);
            } else {
                result.push(a[ap ]);
            }
        } else if (!(ap < aLen)){
            while(bp < bLen){
                result.push(b[bp ]);
            }
        } else if (!(bp < bLen)){
            while(ap < aLen){
                result.push(a[ap ]);
            }
        }
    }
    return result;
}

第二种:

复制代码 代码如下:

/**Lu Jun*/
function merge(arr1, arr2){

    var i = 0;
    var j = 0;
    var c = 0;
    var k;
    var len1 = arr1.length;
    var len2 = arr2.length;
    var arr = [];
    for(;i        if( arr1[i] > arr2[j]  ){
            arr.push( arr2[j] );
            j ;
        }else{
            arr.push( arr1[i] );
            i ;
        }
        //if(i==len1 || j==len2){
        //    break;
        //}
    }

    if(i==len1){
        //arr = arr.concat(arr2.slice(j));

        for(k=j; k            arr.push( arr2[k] );
        }
    }

    if(j==len2){
        //arr = arr.concat(arr1.slice(i))
        for(k=i; k            arr.push( arr1[k] );
        }

    }

    return arr;
}

第三种:

复制代码 代码如下:

/*金锐的*/
function merge(a,b){
    var x = 0;
    var l = 0;
    var list = [];
    var aLen = a.length;
    var bLen = b.length;

    for(var i = 0; i < bLen; i ){
        for(var j = x; j < aLen; j ){
            if(b[i] < a[j]){
                list.push(b[i]);
                l = i;
                break;
            }else{               
                list.push(a[j]);
                x ;
            }
        }    
    }           

    if(x == a.length){
        for(var y = l; y < bLen; y ){
            list.push(b[y]);
        }
    }else{
        for(var z = x; z < aLen; z ){
            list.push(a[z]);
        }
    }

    return list;
}

经过测试2个有序20W长度的数组归并耗时都在15毫秒以下。

以下有几条经验(在大量操作的时候才能体现,平时不需要做这样的优化。代码可读性还是第一原则)

1:数组的concat方法比直接for循环push要慢。

2:for循环比while循环快。

3:var a = b || 3; //这种操作很消耗时间

4: break,continue 在已确定不需要再循环时很耗时。

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