引言
本篇是排序算法的第五篇,归并排序。
1、算法步骤
归并算法采用分治策略,如下图(图片来自网络):
从上图可以看出算法步骤是:
1、先将待排序序列用二分法形式递归的分开。
2、再将分开的数据排序后递归的合并。
2、时间复杂度
平均时间复杂度O(n log n)
3、算法实现
public class MergeSort {
public static void main(String[] args) {
int[] numbers = {
12,2,24,30,6,16};
int[] result = MergeSort.sort(numbers);
StringBuffer stringBuffer = new StringBuffer();
for (int i = 0; i < result.length; i++) {
stringBuffer.append(result[i] + " ");
}
System.out.println(stringBuffer.toString());
}
public static int[] sort(int[] number){
//重新copy一个新数组,不影响参数
int[] needSort = Arrays.copyOf(number, number.length);
//无需排序
if(needSort.length < 2){
return needSort;
}
//下面步骤是对半分开
int middle = (int)Math.floor(needSort.length/2);
int[] left = Arrays.copyOfRange(needSort, 0, middle);
int[] right = Arrays.copyOfRange(needSort,middle,needSort.length);
//递归对半先分开,再并排序
return merge(sort(left),sort(right));
}
//排序
protected static int[] merge(int[] left,int[] right){
//新数组存放结果集
int[] result = new int[left.length + right.length];
int i = 0;
while (left.length > 0 && right.length > 0){
if(left[0] < right[0]){
result[i++] = left[0];
left = Arrays.copyOfRange(left,1,left.length);
} else {
result[i++] = right[0];
right = Arrays.copyOfRange(right,1,right.length);
}
}
while (left.length > 0){
result[i++] = left[0];
left = Arrays.copyOfRange(left,1,left.length);
}
while (right.length > 0){
result[i++] = right[0];
right = Arrays.copyOfRange(right,1,right.length);
}
return result;
}
}
结束语
下一篇:将介绍排序算法之快速排序。