学步园

package main

import (
	"fmt"
)

var tmp [len(src)]int
var src = [7]int{2, 4, 9, 7, 6, 1, 9}

//对排序好的分数组进行合并
func Merge(left, m, right int) {
	i := left
	j := left //标示把排序好的数放到临时数组的那个index
	w := m + 1

	//比较，把比较小的数字放到临时数组中去
	for i <= m && w <= right {
		if src[i] >= src[w] {
			tmp[j] = src[w]
			w += 1
		} else {
			tmp[j] = src[i]
			i += 1
		}
		j += 1
	}

	//把剩余数组中的数字依次copy到临时数组中去
	for i <= m {
		tmp[j] = src[i]
		i += 1
		j += 1
	}
	for w <= right {
		tmp[j] = src[w]
		w += 1
		j += 1
	}

	//把临时数组的数据copy到原数组中
	for left <= right {
		src[left] = tmp[left]
		left += 1
	}
}

func MergeSort(left, right int) {
	if left >= right {
		return
	}

	m := (left + right) / 2
	MergeSort(left, m)
	MergeSort(m+1, right)
	Merge(left, m, right)
}

func main() {
	MergeSort(0, len(src)-1)
	fmt.Println(src)
}

归并排序是经典的divide conquer算法。基本思想很简单，但是写代码的时候，要小心各种边界值和index的变换。