各种排序算法

基础才是最重要的， 好久不写排序了，今天写了一下还是各种报错。。。。

要养成习惯，每天至少做一道算法题

 

//复习各种排序
public class SortApp {

    public static void main(String[] args) {
        int[] a = {5,23,7,18,56,2,36,5,3,9,6,4,1};
        SortApp app = new SortApp();
        //app.quickSort(a);
        //app.selectSort(a);
        //app.insertSort(a);
        app.bubbleSort(a);
        app.display(a);
    }
    
    //快速
    void quickSort(int[] a){
        quickSort(a, 0, a.length - 1);
    }
    
    private void quickSort(int[] a, int left, int right){
        if(left >= right) return;
        int pivot = left;
        int i = left, j = right + 1;
        
        while(i<j){
            while(a[++i] < a[pivot] && i < right);
            while(a[--j] > a[pivot] && j > 0);
            if(i<j)swap(a, i, j);
        }
        swap(a,pivot, j);
        
        quickSort(a, left, j-1);
        quickSort(a, j+1, right);
    }
    
    //冒泡
    void bubbleSort(int[] a){
        for(int i = 0; i < a.length; i++){
            for(int j = 1; j < a.length - i; j++){
                if(a[j-1] >= a[j]){
                    swap(a,j-1,j);
                }
            }
        }
    }
    
    //插入
    void insertSort(int[] a){
        for(int i = 1; i < a.length; i++){
            int current = a[i];
            //pointer for the previous element of i
            int j = i-1;
            while(j>=0 && a[j] > current){
                a[j+1] = a[j];
                j--;
            }
            
            //now j points to the element which is smaller than a[i]
            a[j+1] = current;
        }
    }
    
    //选择
    void selectSort(int[] a){
        for(int i = 0; i < a.length; i++){
            int min = i;
            for(int j = i+1; j < a.length; j++){
                if(a[j] < a[min]) min = j;
            }
            swap(a, i, min);
        }
    }
    
    private void swap(int[] a, int i, int j){
        int tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;
    }
    
    private void display(int[] a){
        for(int i: a){
            System.out.print(" " + i);
        }
        System.out.println("");
    }
}