面试题2：自己实现七个排序算法

Posted 2020-09-17 wxquare的学习笔记

冒泡排序：

template<typename Dtype>
void bubbleSort(Dtype arr[], int len) {
    if (len < 2)
        return;

    bool isSorted;
    for (int i = 0; i < len - 1; i++) {
        isSorted = true;
        for (int j = 0; j < len - 1; j++) {
            if (arr[j] > arr[j + 1]) {
                isSorted = false;
                std::swap(arr[j], arr[j + 1]);
            }
        }
        if(isSorted) return;
    }
}

选择排序：

void selectSort(vector<int>& arr) {
    int n = arr.size();
    if (n <= 1) return;
    for (int i = 0; i < n-1; i++) {
        int minIndex = i;
        for (int j = i + 1; j < n; j++) {
            if (arr[j] < arr[minIndex])
                minIndex = j;
        }
        if(minIndex != i)
            swap(arr[i],arr[minIndex]);
    }
}

插入排序：

    //插入排序
    void insertSort(int* arr, int len) {
        if (len < 2)
            return;
        int temp,j;
        for (int i = 1; i < len; i++) {
            if (arr[i] < arr[i - 1]) {
                temp =arr[i];
                for (j = i - 1; j >= 0 && arr[j] > temp; j--) {
                    arr[j + 1] = arr[j];
                }
                arr[j+1] = temp;
            }
        }
    }

快速排序：

template<typename Dtype>
void quickSort(Dtype arr[], int left, int right) {
    if (left >= right) return;
    Dtype pivotVal = arr[left];
    int l = left;
    int r = right;
    while(l < r){
        while(l < r && arr[r] >= pivotVal) r--;
        arr[l] = arr[r];
        while(l < r && arr[l] <= pivotVal) l++;
        arr[r] =arr[l];
    }
    arr[l] = pivotVal;
    quickSort(arr, left, l- 1);
    quickSort(arr, l + 1, right);
}

template<typename Dtype>
void quickSort(Dtype arr[], int len) {
    if (len < 2)
        return;
    quickSort<Dtype>(arr, 0, len - 1);
}

 归并排序：

class MergeSort {
private:
    void mergeSort(vector<int>&arr, int left, int right) {
        if (left >= right)
            return;

        int mid = (left + right) / 2;
        mergeSort(arr, left, mid);
        mergeSort(arr, mid + 1, right);
        merge(arr, left, mid, right);
    }

    void merge(vector<int>&arr, int left, int mid, int right) {
        int* temp = new int[right - left + 1];

        int i = left;
        int j = mid + 1;
        int k = 0;
        while (i <= mid && j <= right) {
            if (arr[i] <= arr[j])
                temp[k++] = arr[i++];
            else
                temp[k++] = arr[j++];
        }
        while (i <= mid)
            temp[k++] = arr[i++];
        while (j <= right)
            temp[k++] = arr[j++];

        int n = right - left + 1;
        for (int i = 0; i < n; i++) {
            arr[left + i] = temp[i];
        }

        delete[] temp;
    }
public:
    void mergeSort(vector<int>& arr) {
        int n = arr.size();
        if (n <= 1)
            return;
        mergeSort(arr, 0, n - 1);
    }
};

堆排序：

class HeapSort {
private:
    void heapAdjust(vector<int>&arry, int start, int size) {

        int lchild = 2 * start + 1, rchild = lchild + 1;
        while (rchild < size) {
            if (arry[start] >= arry[lchild] && arry[start] >= arry[rchild])
                return;

            if (arry[lchild] >= arry[rchild]) {
                swap(arry[start], arry[lchild]);
                start = lchild;
            } else {
                swap(arry[start], arry[rchild]);
                start = rchild;
            }
            lchild = start * 2 + 1;
            rchild = lchild + 1; //重新计算子树位置
        }

        if (lchild < size && arry[lchild] > arry[start]) //只有左子树且子树小于自己
        {
            swap(arry[lchild], arry[start]);
        }
    }
public:
    void heapSort(vector<int>& arr) {
        int n = arr.size();
        if (n <= 1)
            return;

        //建立大顶堆
        for (int i = n / 2 - 1; i >= 0; i--) {
            heapAdjust(arr, i, n);
        }

        //依次选择最大的数
        for (int i = n - 1; i >= 0; i--) {
            swap(arr[0], arr[i]);
            heapAdjust(arr, 0, i - 1);
        }
    }
};

 希尔排序：

    //shell排序
    void shellSort(int* arr, int len) {
        int gap = len;
        while (gap > 1) {
            gap = (gap + 1) / 2;
            for (int i = 0; i < len - gap; i++) {
                if (arr[i + gap] < arr[i]) {
                    swap(arr[i + gap], arr[i]);
                }
            }
        }
    }