Question

I'm attempting to build out a monkey-patched version of mergeSort but I'm running into errors every single time. I've ran through debugger a few times and it looks like everything is sorting properly until the last step where I jump to a line in a loader.js file.

Can anyone help me check this out? Thanks in advance!


Array.prototype.mergeSort = function(callback) {
    if (this.length <= 1) return this;

    if (!callback) {
        callback = function(x, y) {
            if (x > y) return -1;
            else if (x < y) return 1;
            else return 0;
        };
    }

    const mid = Math.floor(this.length / 2);
    const sortedLeft = this.slice(0, mid).mergeSort(callback);
    const sortedRight = this.slice(mid).mergeSort(callback);

    return sortedLeft.merge(sortedRight, callback);
};

Array.prototype.merge = function(arr, callback) {
    let merged = [];

    while (this.length > 0 || arr.length > 0) {
        if (callback(this[0], arr[0]) < 0) {
            merged.push(arr.shift());
            break;
        } else if (callback(this[0], arr[0]) >= 0) {
            merged.push(this.shift());
            break;
        }
    }

    merged = merged.concat(this);
    merged = merged.concat(arr);

    return merged;
};

Answer 1

当任一列表为空时，合并循环应停止：您应该输入{p>而不是while (this.length > 0 || arr.length > 0)

while (this.length > 0 && arr.length > 0)

此外，每次存储到break数组后，您都不应从循环中merge，并且将元素进行两次比较是多余的。

这是更正的版本：

Array.prototype.merge = function(arr, callback) {
    let merged = [];

    while (this.length > 0 && arr.length > 0) {
        if (callback(this[0], arr[0]) < 0) {
            merged.push(arr.shift());
        } else {
            merged.push(this.shift());
        }
    }
    merged = merged.concat(this);
    return merged.concat(arr);
};

但是请注意，您的merge方法按降序对数组进行排序，默认的callback函数也按降序对元素进行比较，从而导致数组按巧合顺序按升序进行排序。您可能想要简化此过程，并在null中接受merge回调函数。

这是一个更通用的版本：

Array.prototype.mergeSort = function(callback) {
    if (this.length <= 1)
        return this;

    const mid = this.length >> 1;
    const sortedLeft = this.slice(0, mid).mergeSort(callback);
    const sortedRight = this.slice(mid).mergeSort(callback);

    return sortedLeft.merge(sortedRight, callback);
};

Array.prototype.merge = function(arr, callback) {
    let merged = [];

    if (callback) {
        while (this.length > 0 && arr.length > 0) {
            if (callback(this[0], arr[0]) <= 0) {
                merged.push(this.shift());
            } else {
                merged.push(arr.shift());
            }
        }
    } else {
        while (this.length > 0 && arr.length > 0) {
            if (this[0] <= arr[0]) {
                merged.push(this.shift());
            } else {
                merged.push(arr.shift());
            }
        }
    }
    return merged.concat(this).concat(arr);
};

Infinite loop while building mergesort in JavaScript

1 个答案: