java算法

1、递归

package com.算法1;

public class 递归 {
    
    public static String daoxu(String str){
        if(str == null || str.length() < 2){
            return str;
        }
        String temp = str.substring(1,str.length());
        char end = str.charAt(0);
        
        return daoxu(temp) + end;
    }
    
    public static void main(String[] args) {
        String str = "abcd";
        String temp = daoxu(str);
        System.out.println(temp);
    }
}

2、冒泡

package com.算法1;

public class 冒泡 {
    public static int[] maopao(int arry[]){
        for(int i = 0 ; i < arry.length ; i++){
            for(int j = i+1 ; j < arry.length ; j++){
                if(arry[i] > arry[j]){
                    int temp = arry[i];
                    arry[i] = arry[j];
                    arry[j] = temp;
                }
            }
        }
        
        return arry;
    }
    
    
    public static void main(String[] args) {
        int [] arry = {6,8,1,11,22,56,33,23,66,12};
        maopao(arry);
        for(int i = 0 ; i < arry.length; i++){
            System.out.println(arry[i]);
        }
    }
}

3、二分查找

package com.算法1;

public class 二分查找 {
    
    //找出值等于num的下标
    public static int erfenchaozhao(int arry[], int num){
        int low = 0;
        int heigh = arry.length - 1;
        int middle = 0;
        while(low < heigh){
             middle = (low + heigh)/2;
            if(arry[low] < num){
                low ++;
            }else if(arry[heigh] > num){
                heigh--;
            }else{
                return middle;
            }
        }
        
        return middle;
    }
    
    public static void main(String[] args) {
        int [] arry = {1,3,4,5,7,9,10,12,15,18,30,60};
        int index = erfenchaozhao(arry,12);
        System.out.println(index);
    }
}

4、快速排序

package com.算法1;

 

public class 快速排序 {

 

/**

* 通过一趟排序将要排序的数据分割成独立的两部分，

* 其中一部分的所有数据都比另外一部分的所有数据都要小，

* 然后再按此方法对这两部分数据分别进行快速排序，整个排序过程可以递归进行，

* 以此达到整个数据变成有序序列

*/

static void quicksort(int arry[], int left, int right) {

int dp;

if (left < right) {

dp = partition(arry, left, right);

System.out.println(dp+".....");

quicksort(arry, left, dp - 1);

quicksort(arry, dp + 1, right);

}

}

 

static int partition(int arry[], int left, int right) {

int pivot = arry[left];

while (left < right) {

while (left < right && arry[right] >= pivot)

right--;

if (left < right)

arry[left++] = arry[right];

while (left < right && arry[left] <= pivot)

left++;

if (left < right)

arry[right--] = arry[left];

}

arry[left] = pivot;

return left;

}

 

public static void main(String[] args) {

int [] arry = {16,8,21,1,15,56,33,23,66,12};

int left = 0;

int right = arry.length - 1;

quicksort(arry, left, right);

 

for(int i = 0 ; i < arry.length ; i++){

System.out.println(arry[i]);

}

 

}

}