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class Solution {
    public int[] sortArray(int[] nums) {
        mergeSort(nums, nums.clone(), 0, nums.length - 1);
        return nums;
    }

    private void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }

    // Bubble Sort 最大值到最后一个位置, 次大到倒数第二个...
    public void bubbleSort(int[] nums) {
        int inPlaceCount = 0;
        // We have nums.length numbers to process in order to let each of them be in
        // the right place
        for (int i = 0; i < nums.length - 1; i++) {
            boolean isSorted = true;
            // We don't bother the nums that are in place which is the last
            // "inPlaceCount" nums.
            for (int j = 0; j < nums.length - inPlaceCount - 1; j++) {
                if (nums[j] > nums[j + 1]) {
                    isSorted = false;
                    swap(nums, j, j + 1);
                }
            }
            // End the outer for loop earlier.
            if (isSorted)
                break;
            inPlaceCount += 1;
        }
        return nums;
    }

    // Selection Sort 第0个位置最小的坐,第1个位置次小的坐...
    public void selectionSort(int[] nums) {
        for (int i = 0; i < nums.length - 1; i++) {
            int minIdx = i;
            for (int j = i; j < nums.length; j++) {
                if (nums[j] < nums[minIdx]) {
                    minIdx = j;
                }
            }
            swap(nums, minIdx, i);
        }
        return nums;
    }

    // Insertion Sort 当前位置的值比前一个小,那就换到前面,一直到换不动为止
    public void insertionSort(int[] nums) {
        for (int i = 1; i < nums.length; i++) {
            for (int j = i; j > 0; j--) {
                if (nums[j] < nums[j - 1]) {
                    swap(nums, j, j - 1);
                } else {
                    break;
                }
            }
        }
        return nums;
    }

    // Quick Sort
    private void quickSort(int[] nums, int start, int end) {
        if (start >= end) {
            return;
        }
        int pivot = start, left = start + 1, right = end;
        while (left <= right) {
            if (nums[left] > nums[pivot] && nums[right] < nums[pivot]) {
                swap(nums, left, right);
                left += 1;
                right -= 1;
                continue;
            }
            if (nums[left] <= nums[pivot]) {
                left += 1;
            }
            if (nums[right] >= nums[pivot]) {
                right -= 1;
            }
        }
        swap(nums, pivot, right);
        boolean isLeftShorter = right - start <= end - right ? true : false;
        if (isLeftShorter) {
            quickSort(nums, start, right - 1);
            quickSort(nums, right + 1, end);
        } else {
            quickSort(nums, right + 1, end);
            quickSort(nums, start, right - 1);
        }
    }

    // Merge Sort 给一个范围, 能把这个范围内的数字给sort好. 注意nums和aux往下传递的时候要颠倒位置.
    private void mergeSort(int[] nums, int[] aux, int start, int end) {
        if (start >= end) {
            return;
        }
        int mid = start + (end - start) / 2;
        mergeSort(aux, nums, start, mid);
        mergeSort(aux, nums, mid + 1, end);
        merge(nums, aux, start, mid, end);
    }

    private void merge(int[] nums, int[] aux, int left, int middle, int right) {
        int ptr = left, ptrOne = left, ptrTwo = middle + 1;
        while (ptrOne <= middle && ptrTwo <= right) {
            if (aux[ptrOne] <= aux[ptrTwo]) {
                nums[ptr++] = aux[ptrOne++];
            } else {
                nums[ptr++] = aux[ptrTwo++];
            }
        }
        while (ptrOne <= middle) {
            nums[ptr++] = aux[ptrOne++];
        }
        while (ptrTwo <= right) {
            nums[ptr++] = aux[ptrTwo++];
        }
    }
}