归并排序（mergeSort）的kotlin实现

归并排序的核心是把两个有序数组合并为一个新的有序数组,具体操作就是通过递归的方式层层执行核心方法。

fun mergeSort(array: IntArray): IntArray {
    //嵌套函数
    fun merge(left: IntArray, right: IntArray): IntArray {

        val ret = IntArray(left.size + right.size)
        var i = 0
        var p = 0
        var q = 0
        while (p < left.size && q < right.size) {
            if (left[p] <= right[q]) {
                ret[i++] = left[p++]
            } else {
                ret[i++] = right[q++]
            }
        }

        if (p == left.size) {
            for (index in q until right.size) {
                ret[i++] = right[index]
            }
        } else {
            for (index in p until left.size) {
                ret[i++] = left[index]
            }

        }

        return ret
    }

    if (array.size < 2)
        return array

    val middle = array.size / 2
    val left = array.copyOfRange(0,middle)
    val right = array.copyOfRange(middle,array.size)
    return merge(mergeSort(left), mergeSort(right))
}

kotlin小白，有错误请不吝指教~