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Copy pathNthElement.java
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58 lines (51 loc) · 1.7 KB
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package utils;
public final class NthElement {
public static int findKthLargest(int[] nums, int k) {
return select(nums, k - 1);
}
// Quick Select
private static int select(int[] nums, int k) {
int left = 0, right = nums.length - 1;
while (true) {
if (left == right) {
return nums[left];
}
int pivotIndex = medianOf3(nums, left, right);
pivotIndex = partition(nums, left, right, pivotIndex);
if (pivotIndex == k) {
return nums[k];
} else if (pivotIndex > k) {
right = pivotIndex - 1;
} else {
left = pivotIndex + 1;
}
}
}
//Use median-of-three strategy to choose pivot
private static int medianOf3(int[] nums, int left, int right) {
final int mid = left + (right - left) / 2;
if (nums[right] > nums[left]) { swap(nums, left, right); }
if (nums[right] > nums[mid]) { swap(nums, right, mid); }
if (nums[mid] > nums[left]) { swap(nums, left, mid); }
return mid;
}
private static int partition(int[] nums, int left, int right, int pivotIndex) {
final int pivotValue = nums[pivotIndex];
swap(nums, pivotIndex, right);
int index = left;
for (int i = left; i < right; ++i) {
if (nums[i] > pivotValue) {
swap(nums, index, i);
++index;
}
}
swap(nums, right, index);
return index;
}
private static void swap(int[] nums, int a, int b) {
final int temp = nums[a];
nums[a] = nums[b];
nums[b] = temp;
}
private NthElement() {}
}