归并排序

function merger( a, b ){
    var array = [], m = a.length, n = b.length;
    for(var i = 0, j = 0; i < m && j <n ){
        if(a[i] > b[j]){
            array.push(b[j]);
            ++j;
        }else{
            array.push( a[i] );
            ++i;
        }
    }
    while( i < m ){
        array.push( ret[i] );
        ++i;
    }
    while( j < n ){
        array.push( ret[j] );
        ++j;
    }
    return array;
}
function mergerSort(arr){
    if(arr.length <= 1) return arr;
    var position = Math.floor(arr.length/2);
    var a = arr.slice(0 , position);
    var b = arr.slice (position);
    return merger( mergerSort(a), mergerSort(b) );
}