912. Sort an Array

题目

Given an array of integers nums, sort the array in ascending order.

我的想法

快排模板
注意！！！为了使左右指针错开，以防止死循环，快排的所有判断都要带等号！

class Solution {
    public List<Integer> sortArray(int[] nums) {
        quickSort(nums, 0, nums.length - 1);
        List<Integer> res = new ArrayList<>();
        for(int i = 0; i < nums.length; i++) {
            res.add(nums[i]);
        }
        return res;
    }
    
    private void quickSort(int[] nums, int start, int end) {
        if(start >= end) {
            return;
        }
        int left = start, right = end;
        int pivot = nums[(start + end) / 2];
        while(left <= right) {
            while(left <= right && nums[left] < pivot) {
                left++;
            }
            while(left <= right && nums[right] > pivot) {
                right--;
            }
            if(left <= right) {
                int temp = nums[left];
                nums[left] = nums[right];
                nums[right] = temp;
                left++;
                right--;
            }

        }
        quickSort(nums, start, right);
        quickSort(nums, left, end);
    }
}

归并模板
注意！！！在merge数组时，因为是在每段内排序，index是从start开始的！

class Solution {
    public List<Integer> sortArray(int[] nums) {
        int[] temp = new int[nums.length];
        mergeSort(nums, 0, nums.length - 1, temp);
        List<Integer> res = new ArrayList<>();
        for(int i = 0; i < nums.length; i++) {
            res.add(nums[i]);
        }
        return res;
    }
    
    private void mergeSort(int[] nums, int start, int end, int[] temp) {
        if(start >= end) {
            return;
        }
        mergeSort(nums, start, (start + end) / 2, temp);
        mergeSort(nums, (start + end) / 2 + 1, end, temp);
        merge(nums, start, end, temp);
    }
    
    private void merge(int[] nums, int start, int end, int[] temp) {
        int middle = (start + end) / 2;
        int leftIndex = start;
        int rightIndex = middle + 1;
        //注意！！！是在每段内排序，index是从start开始的！！！
        int index = start;
        while(leftIndex <= middle && rightIndex <= end) {
            if(nums[leftIndex] < nums[rightIndex]) {
                temp[index++] = nums[leftIndex++];
            } else {
                temp[index++] = nums[rightIndex++];
            }
        }
        while(leftIndex <= middle) {
            temp[index++] = nums[leftIndex++];
        }
        while(rightIndex <= end) {
            temp[index++] = nums[rightIndex++];
        }
        //同上
        for(int i = start; i <= end; i++) {
            nums[i] = temp[i];
        }    
    }
}

解答