常用排序算法总结

1. 冒泡排序

void bubbleSort(int a[], int size){
int n = size - 1;
for(int i = 0; i < n; i++){
for(int j = n; j > i; j--){
if(a[j] < a[j-1]){
swap(&a[j], &a[j-1]);
}
}
}
}

2. 选择排序

void selectSort(int a[], int size){
int n = size - 1;
int min;
for(int i = 0; i < n; i++){
min = i;
for(int j = i + 1; j < size; j++){
if(a[j] < a[min])
min = j;
}
swap(&a[i], &a[min]);
}
}

3. 插入排序

void insertSort(int a[], int size){
int n = size - 1;
int obj;
int j;
for(int i = 1; i <= n; i++){
obj = a[i];
j = i-1
for(; j >= 0; j--)
if(obj < a[j]) a[j+1] = a[j];
else break;
a[j+1] = obj;    //细心：j+1
}
}

4. 希尔排序

void shellSort(int a[], int size){
//int n = sizeof(A) / sizeof(int);
int i, j, get;
int h = 0;
while (h <= n)                    // 生成初始增量
{
h = 3*h + 1;
}
while (h >= 1)
{
for (i = h; i < n; i++)
{
j = i - h;
get = A[i];
while ((j >= 0) && (A[j] > get))
{
A[j + h] = A[j];
j = j - h;
}
A[j + h] = get;
}
h = (h - 1) / 3;             // 递减增量
}
}

5. 归并排序

void merge(int a[], int left, int mid, int right){
int ln = mid - left + 1;
int rn = right - mid;
int l[ln+1];
int r[rn+1];
for(int i = 0; i < ln; i++){
l[i] = a[left+i];
}
for(int i = 0;i < rn; i++){
r[i] = a[mid+1+i];
}
l[ln] = INT_MAX;
r[rn] = INT_MAX;
int m  = 0, n = 0;
for(int i = left; i <= right; i++){
if(l[m] < r
){
a[i] = l[m];
m++;
} else {
a[i] = r
;
n++;
}
}
}
//边界问题：函数参数含义需要非常清晰
void mergeSort(int a[], int left, int right){
int mid = (left + right)/2;
if(left < right){
mergeSort(a, left, mid);
mergeSort(a, mid+1, right);
merge(a, left, mid, right);
}
}

6. 堆排序

// 堆数组中对于节点i,其父节点(i - 1)/2
// 左子节点i*2+1， 右子节点i*2+2
void heapDown(int a[], int root, int size){
int child = root*2 + 1;
int rChild = child + 1;
if(child < size){
if(rChild < size && a[rChild] > a[child])
child++;
if(a[child] > a[root]){
swap(&a[child], &a[root]);
heapDown(a, child, size);
}
}
}

void heapSort(int a[], int size){
//size/2 为最大非叶子节点
for(int i = size/2; i >=0; i--){
heapDown(a, i, size);
}
for(int i = size - 1; i > 0; i--){
swap(&a[0], &a[i]);
heapDown(a, 0, i);//i 非 i-1
}
}

7. 快速排序

void quickSort(int a[], int left, int right){
if(left < right){
int key = a[left]; //基准
int l = left;
int r = right;
while(l < r){
while(a[r] > key && l<r)r--;
a[l] = a[r];
while(a[l] <= key && l<r)l++;
a[r] = a[l];
}
a[l] = key;
quickSort(a, left, l-1);
quickSort(a, l+1, right);
}
}