Merge Sort
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/*
本算法答案由上岸科技提供。
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*/
public class Solution {
public int[] sortArray(int[] nums) {
// use a shared temp array, the extra memory is O(n) at least
int[] temp = new int[nums.length];
mergeSort(nums, 0, nums.length - 1, temp);
return nums;
}
private void mergeSort(int[] nums, int start, int end, int[] temp) {
if (start >= end) {
return;
}
int mid = (start + end) / 2;
mergeSort(nums, start, mid, temp);
mergeSort(nums, mid + 1, end, temp);
merge(nums, start, mid, end, temp);
}
private void merge(int[] nums, int start, int mid, int end, int[] temp) {
int left = start;
int right = mid + 1;
int index = start;
// merge two sorted subarrays in A to temp array
while (left <= mid && right <= end) {
if (nums[left] < nums[right]) {
temp[index++] = nums[left++];
} else {
temp[index++] = nums[right++];
}
}
while (left <= mid) {
temp[index++] = nums[left++];
}
while (right <= end) {
temp[index++] = nums[right++];
}
// copy temp back to A
for (index = start; index <= end; index++) {
nums[index] = temp[index];
}
}
}
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