JavaScript的归并排序

递归方法在JS中受到了堆栈深度的限制，在数目特别大的时候会抛出异常，所以JS使用的归并排序需要使用非递归的版本。

// non in-place
mergeSort = function(source){
    const mergeArray = function(left,right){
        var result = [];
        while(left.length * right.length > 0){
            left[0]>right[0]?result.push(right[0]):result.push(left[0]);
        }
        result = result.concat(left,right);
        if(left.length) left.length = 0;
        if(right.length) right.length = 0;
        return result;
    }
    var mergeList = [];
    for(let i = 0;i<source.length;i++){
        var temp = [];
        temp.push(source[i])
        mergeList.push(temp);
    }	
    while(mergeList.length>1){
        for(let i = 0; i<Math.floor(mergeList.length/2);i++){
            mergeList[i]=mergeArray(mergeList[i],mergeList[mergeList.length-1-i]);
        }
        mergeList.length = Math.ceil(mergeList.length/2);
    }
    return mergeList[0];
}

// in-place
Array.prototype.mergeSort = function () {
    var mergeArray = function (arr1, arr2) {
        var result = [];
        if (!(arr1 instanceof Array)) {
            arr1 = [arr1];
        }
        if (!(arr2 instanceof Array)) {
            arr2 = [arr2];
        }
        while (arr1.length * arr2.length > 0) {
            if (arr1[0] > arr2[0]) {
                result.push(arr2.shift());
            } else {
                result.push(arr1.shift());
            }
        }
        result = result.concat(arr1, arr2)
        if (arr1.length > 0) {
            arr1.length = 0;
        }
        if (arr1.length > 0) {
            arr1.length = 0;
        }
        return result;
    }
    while (this.length > 1) {
        for (let i = 0; i < Math.floor(this.length / 2); i++) {
            this[i] = mergeArray(this[i], this[this.length - 1 - i]);
        }
        this.length = Math.ceil(this.length / 2);
    }
    for (var i = 1; i <= this[0].length; i++) {
        this[i] = this[0][i - 1];
    }
    this.shift();
}