Java插入排序：“相同”变量得到不同的结果

Question

I was doing an insertion sort using Java. For example, if I have an integer array {8,7,6,5,4,3,2,1},

This will give me the result which is wrong: 7,6,5,4,3,2,1,8 picture

public static int[] insertionSort(int[] list) {
    int[] insertionList = list.clone();
    for(int i = 1; i < insertionList.length; i++) {
        int temp = insertionList[i];
        int j = i - 1;
        while(j >= 0 && insertionList[j] > insertionList[i]) {
            insertionList[j + 1] = insertionList[j];
            j--;
        }
        insertionList[j + 1] = temp;
    }
    return insertionList;
}

And this will give me the result which I wanted: 1,2,3,4,5,6,7,8 picture

public static int[] insertionSort(int[] list) {
    int[] insertionList = list.clone();
    for(int i = 1; i < insertionList.length; i++) {
        int temp = insertionList[i];
        int j = i - 1;
        while(j >= 0 && insertionList[j] > temp) {
            insertionList[j + 1] = insertionList[j];
            j--;
        }
        insertionList[j + 1] = temp;
    }
    return insertionList;
}

Just wondering what different between insertionList[i] and temp . I wrote two println statements to test these, but they also show the same number.

Thanks!!!!!

Answer 1

The difference is that the 'insertionList' gets modified inside the while loop. When you set the temp variable to 'insertionList[i]' the value of temp remains the same throughout the while loop.

Answer 2

while(j >= 0 && insertionList[j] > insertionList[i]) {
            insertionList[j + 1] = insertionList[j];
            j--;
        }

the wrong is here. insertionList[j + 1] = insertionList[j]

in the first execution, j + 1 = i, and it will change the value of insertionList[i]

and it will effect to your condition.

insertionList[j] > insertionList[i]

So it should be change to temp variable.

Answer 3

while(j >= 0 && insertionList[j] > insertionList[i]) In this line you are comparing with the ith element of insertionList and during the iteration in while loop insertionList[j + 1] = insertionList[j]; this code might change the value insertionList[i] was holding. But when you are using temp variable then for the whole iteration the value for comparison here insertionList[j] > temp does not change. That's why you are getting different output.