java实现归并排序算法

今天药忘吃喽~ 2022-05-09 00:28 236阅读 0赞

前面我们讲了[归并排序算法][Link 1]，接下来我们来用java代码实现呗，如下

package ttt;
    
    import java.util.Arrays;
    
    public class MergeSort {
    	public static int[] lastMergeSort(int[] list1,int[] list2) {
    	    int i = 0, j = 0, k = 0;
    	    int [] temp = new int[list1.length + list2.length];
    	    while (i < list1.length && j < list2.length) {
    	    	if (list1[i] <= list2[j]) {
    	            temp[k++] = list1[i++];
    	    	}else {
    	        	temp[k++] = list2[j++];
    	        }
    	    }
    	    
        	if (i == list1.length) {
        		while(j <list2.length) {
        			temp[k++] = list2[j++];
        		}
    	    }
        	if (j == list2.length) {
        		for(;i <list1.length;)
        			temp[k++] = list1[i++];    		
    	    }
    	    return temp;
    	}
    	
        public static int[] mergeSort(int[] theArray) {
        	if(theArray.length ==1) {
        		return theArray;
        	}
        	int mid = (int)theArray.length/2;
        	int[] leftArray = mergeSort(Arrays.copyOfRange(theArray, 0, mid));//前闭后开区间，这种写法开闭了很多空间，有点浪费，实则可以通过别的写法避免的
        	int[] rightArray = mergeSort(Arrays.copyOfRange(theArray, mid, theArray.length));
        	return lastMergeSort(leftArray, rightArray);
        }
    
        public static void main(String[] args) {
        	int []theArray = {10,1,18,30,23,12,7,5,18,17};
            System.out.print("之前的排序：");
            for(int i = 0; i < theArray.length; i++) {
                System.out.print(theArray[i] + " ");
            }
            int [] larray = {1,4,10};
            int [] rarray = {2,6,8,11,15,18};
    //        int []result_array = lastMergeSort(larray,rarray);
            int []resultArray = mergeSort(theArray);
            System.out.print("归并排序：");
            for(int v : resultArray) {
                System.out.print(v + " ");
            }
        }
    }

运行结果如下

之前的排序：10 1 18 30 23 12 7 5 18 17 归并排序：1 5 7 10 12 17 18 18 23 30

符合预期

[Link 1]: https://blog.csdn.net/stronglyh/article/details/82891473