排序算法(一)

//基本算法
for(i=1;i<list.length;k++){
    //perform the kth pass
    for(j=0;list.length-i;j++){ 
        if(list[j]<list[j+1]){
            swap list[j] with list[j];
        }
    }
}

//改进算法
//如果在某次遍历时没有发生交换，那么就不用进行下一次遍历
for(i=1;i<list.length;k++){
    needNextPass=false;
    for(j=0;list.length-i;j++){ 
        if(list[j]<list[j+1]){
            swap list[j] with list[j];
            needNextPass=true;//need next pass
        }
    }
}

 public static void mergeSort(int[] list){
     if(list.lenght>1){
         mergeSort(list[0~list.length/2]);
         mergeSort(list[list.length/2+1~list.length-1]);
         
         merge list[0~list.length/2] with list[list.length/2+1~list.length-1];
     }
 }

public  class MergeSort{
    public static void mergeSort(int[] list){
        if(list.length>1){
            int[] firstHalf=new int[list.length/2];
            System.arraycopy(list,0,firstHalf,0,list.length/2);
            mergeSort(firstHalf);
            
            int[] secondHalf=new int[list.length-list.length/2];
            System.arraycopy(list,list.length/2,secondHalf,0,secondHalf.length);
            mergeSort(secondHalf);
         
            int[] temp=merge(firstHalf,secondHalf);
            System.arraycopy(temp,0,list,0,temp.length);
        }
    }
    private static int[] merge(int[] list1,int[] list2){
        int[] temp=new int[list1.length+list2.length];
        
        int current1=0,current2=0,current3=0;
        
        while(current1<list1.length&&current2<list2.length){
            if(list1[current1]<list2[current2])
              temp[current3++]=list1[current1++];
            else
              temp[current3++]=list2[current2++];            
        }
        while(current1<list1.length){
            temp[current3++]=list1[current1++];
        }
        while(current2<list2.length){
            temp[current3++]=list2[current2++];
        }
        
        return temp;
    }
    public static void main(String[] args){
        int[] list={2,3,2,5,6,1,-1,3,14,12};
        mergeSort(list);
        for(int e:list)
        System.out.print(e+" ");
    }
}

public static void quicksort(int[] list){
    if(list.length>1){
        select a pivot;
        patition list into list1 an list2 such that
           all elements in list1 <= pivot and
           all elements in list2 > pivot
        quicksort(list1);
        quicksort(list2);
    }
}

package Algorithm;

public class QuickSort{
    public static void quicksort(int[] list){
        quicksort(list,0,list.length-1);
    }
    public static void quicksort(int[] list,int left,int right){
        if(right>left){
            int temp=list[left];
            int i=left;
            int j=right;

            while(i!=j){
                //顺序很重要，要先从右边开始找 
                while(list[j]>=temp && i<j){
                    j--; 
                }               
                //再找左边的 
                while(list[i]<=temp && i<j){
                    i++; 
                }                  
                //交换两个数在数组中的位置 
                if(i<j){
                  int t=list[i]; 
                  list[i]=list[j]; 
                  list[j]=t;                  
                } 
            }
            //最终将基准数归位 
            list[left]=list[i]; 
            list[i]=temp;

            quicksort(list,left,i-1);
            quicksort(list,i+1,right);
        }
    } 
            
    public static void main(String[] args) {
        int[] list={6,5,3,8,4,9,7};
        quicksort(list);
        for(int u:list)
            System.out.print(u+",");
    }

}