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Copy pathQuickSelect.java
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69 lines (62 loc) · 1.81 KB
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public class QuickSelect {
public int find(int[] array, int k) {
return find(array, 0, array.length - 1, k);
}
int find(int[] array, int low, int high, int k) {
int p = partition(array, low, high);
if (k == p)
return array[k];
if (k < p)
return find(array, low, p - 1, k);
else
return find(array, p + 1, high, k);
}
int partition(int[] array, int low, int high) {
int pivot = array[low];
int i = low + 1;
int j = high;
while (i < j) {
if (array[i] <= pivot)
i++;
if (array[j] >= pivot)
j--;
if (array[i] > pivot && array[j] < pivot) {
swap(array, i, j);
i++;
j--;
}
}
int p = 0;
if (i < array.length && array[i] < array[low]) {
swap(array, low, i);
p = i;
} else {
swap(array, low, i - 1);
p = i - 1;
}
print(array);
return p;
}
void swap(int[] array, int i, int j) {
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
void print(int[] array) {
for (int i = 0; i < array.length; i++)
System.out.print(array[i] + " ");
System.out.println();
}
public static void main(String[] args) {
QuickSelect qs = new QuickSelect();
//int[] array = {9, 2, 1, 0, 5, 3, 7, 6, 8, 4};
int[] array = new int [20];
for (int i = 0; i < array.length; i++)
array[i] = (int) (Math.random() * array.length);
int num = 0;
for (int i = 0; i < array.length; i++) {
num = qs.find(array, i);
System.out.println(i + ": " + num);
}
}
}