我正在完成任务，我需要执行二分查找。但不知何故，我认为我的选择排序存在问题。这里我有一个名为Record的用户定义类。它具有以下属性：
class Record{
String studentId;
int assignment;
int exam;
int total;
String grade;
}
我有这些属性的吸气剂。现在还有另一个名为 GradeBook 的类，其中有一个类型为记录的数组。我通过一个名为loadFromTables的方法手动加载记录数组，如下所示：
private void loadFromTables(){
String[] students = {
"S10","S20","S30","S40","S50", "S60",
"S08","S18","S28","S38","S48", "S58",
"S06","S16","S26","S36","S46", "S56",
};
int[] assignment = {
0, 10, 20, 30, 30, 40,
0, 10, 20, 30, 30, 40,
0, 10, 20, 30, 30, 40,
};
int[] exam = {
0, 39, 44, 44, 54, 59,
1, 40, 45, 45, 55, 60,
2, 41, 46, 46, 56, 58,
};
nrecords = students.length;
gradeBook = new Record[nrecords];
for (int i = 0; i < nrecords; i++ ) {
int t = assignment[i] + exam[i];
String g = calculateGrade(t);
Record r = new Record( students[i], assignment[i], exam[i], t, g );
gradeBook[i] = r;
}
}
现在我想进行二分查找，找到属性 studentId 的记录。但首先我必须对记录数组进行排序。我被告知使用选择排序。所以，我这样做，我认为这就是问题所在，但我似乎无法弄明白......：
private void sortById(){
//Selection Sort
for(int i=0; i<nrecords-1; i++){
int index = i;
for(int j=i+1; j<nrecords; j++){
if((gradeBook[index].studentId).compareTo(gradeBook[j].studentId) > 0){
index = j;
}
Record temp = gradeBook[i];
gradeBook[i] = gradeBook[index];
gradeBook[index] = temp;
}
}
}
这里是我使用的二进制搜索代码，虽然我认为二进制搜索已经正确实现。因为我试图用冒泡排序来做这件事，而这正是我想要的。
public Record find(String id){
//Binary Search
int low = 0;
int high = nrecords - 1;
Record record = null;
while(low <= high){
int mid = (high + low)/2;
if(id.compareTo(gradeBook[mid].studentId) == 0){
record = new Record(id, gradeBook[mid].assignment, gradeBook[mid].exam, gradeBook[mid].total, gradeBook[mid].grade);
return record;
}
else if(id.compareTo(gradeBook[mid].studentId) > 0){
low = mid + 1;
}
else if(id.compareTo(gradeBook[mid].studentId) < 0){
high = mid - 1;
}
}
return record;
}
提前致谢。我知道问题在于选择排序而且它在吃我的脑袋。感谢您的建议！ ：）
答案 0 :(得分：1)
在选择排序中，我们首先遍历子数组并找到子数组中的最小元素，然后在每次迭代中找到Swap当前和最小元素。
您的代码存在问题。
for(int j=i+1; j<nrecords; j++){
if((gradeBook[index].studentId).compareTo(gradeBook[j].studentId) > 0){
index = j;
}
Record temp = gradeBook[i];
gradeBook[i] = gradeBook[index];
gradeBook[index] = temp;
}
您已经正确找到了最小元素，但是当您找到比当前字符串更小的字典时，您在迭代中进行交换。所以在这个循环中，你只需要找到最小元素，并且在执行这个循环后应该进行swap操作。
更正后的代码：
private void sortById(){
//Selection Sort
for(int i=0; i<nrecords-1; i++){
int index = i;
for(int j=i+1; j<nrecords; j++){
if((gradeBook[index].studentId).compareTo(gradeBook[j].studentId) > 0){
index = j;
}
Record temp = gradeBook[i];
gradeBook[i] = gradeBook[index];
gradeBook[index] = temp;
}
}
}