我正在尝试编写一个修改后的选择排序,它选择最大的数字并将其放置在列表的末尾。我遇到了问题。该代码对列表进行了某种排序,但并不完美。这是我运行代码后的结果: 选择排序前:[2,8,7,1,3,5,9,4,6] 选择排序后:[1, 2, 8, 7, 3, 4, 5, 9, 6]
这是我的代码:
public static int[] sort(int[] list) {
int i, j, maxNum, maxInde, temp = 0;
for (i = list.length-1; i >= 0; i--) {
maxNum = list[i];
maxInde = i;
for (j = i; j < list.length; j++) {
if (list[j] < maxNum) {
maxNum = list[j];
maxInde = j;
}
}
if (maxNum < list[i]) {
temp = list[i];
list[i] = list[maxInde];
list[maxInde] = temp;
}
}
return list;
}
我不知道问题出在哪里。
该算法在概念上存在缺陷,因为您从
n-1
向下扫描数组到 0
,并在每次迭代时从子数组 a[n-1,...,i]
中选择最大元素。该子数组应该始终被排序(并且应该由数组的 n-i
最大元素组成)——这类似于经典选择排序的循环不变式——以及要插入当前位置的最大元素应该来自另一个子数组,即 a[i,...,0]
。
另外,正如评论中提到的,不需要返回数组,因为算法可以修改它。
这是固定版本:
int i, j, maxNum, maxInde, temp = 0;
for (i = list.length-1; i >= 0; i--) {
// you start iterating from the end of the list
// which means that the elements between i and the end of the list are sorted
maxNum = list[i];
maxInde = i;
for (j = 0; j < i; j++) {
// you have to iterate through the nonsorted elements
if (list[j] > maxNum) {
maxNum = list[j];
maxInde = j;
}
}
if (maxNum > list[i]) {
// if you found an element that is bigger then the current element
// then it should be set as the current element
temp = list[i];
list[i] = list[maxInde];
list[maxInde] = temp;
}
}
public static void sortArray(int[] a) {
//find max value in this array
for (int i = 0; i < a. length; i++) {
int max=a[0];
int index=0;
for (int j=0; j<a. length-i; j++) {
if (a[j] >max) {
max=a[j];
index=j;
}
}
//change the index
a[index]=a[a.length-(i+1)];
a[a.length-(i+1)]=max; //max value change the last element
}
}
public static void main (String args[]) {
int [] a= {91,13,53,64,48,49,99,35,65,38,62,72};
System.Out.Println (Arrays.toString (ar));
sortArray(ar);
System.Out.Println (Arrays.toString (ar));
}
}
public static int[] selectionSortWithMax(int[] items) {
int size = items.length;
int maxIndex;
for (int i = size - 1; i >= 0; i--) {
maxIndex = i;
for (int j = i; j >= 0; j--) {
if (items[maxIndex] < items[j]) {
maxIndex = j;
}
}
int temp = items[i];
items[i] = items[maxIndex];
items[maxIndex] = temp;
}
return items;
}