3種歸併操做js代碼

/**良哥的*/
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;
}

 

 

/**魯軍*/
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<len1 && j<len2;){
        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<len2; k++){
            arr.push( arr2[k] );
        }
    }
    
    if(j==len2){
        //arr = arr.concat(arr1.slice(i))
        for(k=i; k<len1; k++){
            arr.push( arr1[k] );
        }
        
    }
        
    return arr;
}

 

/*金銳的*/
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;
}

 

通過測試2個有序20W長度的數組歸併耗時都在15毫秒如下。數組

如下有幾條經驗(在大量操做的時候才能體現,平時不須要作這樣的優化。代碼可讀性仍是第一原則)測試

1:數組的concat方法比直接for循環push要慢。優化

2:for循環比while循環快。spa

3:var a = b || 3; //這種操做很消耗時間code

4: break,continue 在已肯定不須要再循環時很耗時。blog

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