Java归并排序算法代码实现

class Solution {
    public int[] sortArray(int[] nums) {
        mergeSort(nums,0,nums.length-1);
        return nums;
    }
    public void mergeSort(int[] nums,int left,int right){
        if(right==left){
            return;
        }
        int center=(left+right)/2;
        mergeSort(nums,left,center);
        mergeSort(nums,center+1,right);
        merge(nums,left,center,right);
    }
    public void merge(int[] nums,int left,int center,int right){
        int i=left;
        int j=center+1;
        int[] temp=new int[right-left+1];
        int count=0;
        while(i<=center && j<=right){
            temp[count++]=nums[i]>nums[j]?nums[j++]:nums[i++];
        }
        while(i<=center){
            temp[count++]=nums[i++];
        }
        while(j<=right){
            temp[count++]=nums[j++];
        }
        for(int k=0;k<temp.length;k++){
            nums[left+k]=temp[k];
        }
    }
}

class Solution {
    public int[] sortArray(int[] nums) {
        for(int l,m,r,step=1;step<nums.length;step*=2){
            l=0;//设置初始值
            while(l<nums.length){//有左边的组
                m=l+step-1;
                if(m+1>=nums.length){//如果没有右边的组，就退出
                    break;
                }
                r=Math.min(l+(step*2)-1,nums.length-1);//获取右边界，取两者的最小值
                merge(nums,l,m,r);//将两个组合并
                l=r+1;//找到下一个左边的组
            }
        }
        return nums;
    }
    public void merge(int[] nums,int left,int center,int right){
        int i=left;
        int j=center+1;
        int[] temp=new int[right-left+1];
        int count=0;
        while(i<=center && j<=right){
            temp[count++]=nums[i]>nums[j]?nums[j++]:nums[i++];
        }
        while(i<=center){
            temp[count++]=nums[i++];
        }
        while(j<=right){
            temp[count++]=nums[j++];
        }
        for(int k=0;k<temp.length;k++){
            nums[left+k]=temp[k];
        }
    }
}