面试算法代码知识梳理系列
面试算法知识梳理(1) – 排序算法
面试算法知识梳理(2) – 字符串算法第一部分
面试算法知识梳理(3) – 字符串算法第二部分
面试算法知识梳理(4) – 数组第一部分
面试算法知识梳理(5) – 数组第二部分
面试算法知识梳理(6) – 数组第三部分
面试算法知识梳理(7) – 数组第四部分
面试算法知识梳理(8) – 二分查找算法及其变型
面试算法知识梳理(9) – 链表算法第一部分
面试算法知识梳理(10) – 二叉查找树
面试算法知识梳理(11) – 二叉树算法第一部分
面试算法知识梳理(12) – 二叉树算法第二部分
面试算法知识梳理(13) – 二叉树算法第三部分
一、概要
最近在看上学时候总结的一些东西,发现之前针对排序、字符串、数组、链表等,总结了一些面试时候常用的算法代码,因此打算整理一下分享给大家。
本文介绍了排序算法的C++
代码实现,所有代码均可通过 菜鸟工具在线编译器 直接运行,算法目录:
- 插入排序
- 希尔排序
- 选择排序
- 冒泡排序
- 计数排序
- 基数排序
- 归并排序
- 快速排序
- 双向扫描的快速排序
- 堆排序
二、代码实现
2.1 插入排序
#include <iostream>
#include <stdexcept>
using namespace std;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
void insertSort(int *p, int length){
if(p == NULL || length <= 0)
throw std::runtime_error("NULL Pointer");
int i,j,temp;
for(i = 1; i < length; i++){
temp = p[i];
for(j = i; j >= 1 && p[j-1] > temp; j--)
p[j] = p[j-1];
p[j] = temp;
}
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
insertSort(a, 6);
printArray(a, 6);
return 0;
}
运行结果:
>> 2, 29, 30, 42, 50, 60,
2.2 希尔排序
#include <iostream>
#include <stdexcept>
using namespace std;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
void insertShell(int *p ,int inc, int length){
if(p == NULL || length <= 0 || inc <= 0 || inc >= length)
throw std::runtime_error("invaild input");
int i,j,temp;
for(i = inc; i < length; i++){
temp = p[i];
for(j = i; j >= inc && p[j-inc] > temp; j -= inc)
p[j] = p[j-inc];
p[j] = temp;
}
}
void shellSort(int *p, int length){
if(p == NULL || length <= 0)
throw std::runtime_error("invaild input");
int inc = length >> 1;
while(inc >= 1){
insertShell(p,inc,length);
inc >>= 1;
}
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
shellSort(a, 6);
printArray(a, 6);
return 0;
}
运行结果:
>> 2, 29, 30, 42, 50, 60,
2.3 选择排序
#include <iostream>
#include <stdexcept>
using namespace std;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
void selectSort(int *p, int length){
if(p == NULL || length <= 0)
throw std::runtime_error("NULL Pointer");
int i,j,mind,t;
for(j = 0; j < length - 1; j++){
mind = j;
for(i = j+1; i < length; i++){
if(p[i] < p[mind])
mind = i;
}
if(mind != j){
t = p[j]; p[j] = p[mind]; p[mind] = t;
}
}
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
selectSort(a, 6);
printArray(a, 6);
return 0;
}
运行结果:
>> 2, 29, 30, 42, 50, 60,
2.4 冒泡排序
#include <iostream>
#include <stdexcept>
using namespace std;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
void bubbleSort(int *p, int length){
if(p == NULL || length <= 0)
throw std::runtime_error("NULL Pointer");
int i,j,t;
for(j = 0; j < length - 1; j++)
for(i = 0; i < length - j - 1; i++){
if(p[i] > p[i+1]){
t = p[i]; p[i] = p[i+1]; p[i+1] = t;
}
}
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
bubbleSort(a, 6);
printArray(a, 6);
return 0;
}
运行结果:
>> 2, 29, 30, 42, 50, 60,
2.5 计数排序
#include <iostream>
#include <stdexcept>
using namespace std;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
void countSort(int *p, int length, int maxNum){
if(p == NULL || length <= 0 )
throw std::runtime_error("NULL Pointer");
int *c = new int[maxNum+1];
int *b = new int[length];
int i;
for(i = 0; i < maxNum+1; i++){
c[i] = 0;
}
for(i = 0; i < length; i++){
if(p[i] > maxNum)
throw std::runtime_error("invaild input");
c[p[i]] += 1;
}
for(i = 1; i < maxNum+1; i++){
c[i] += c[i-1];
}
for(i = length-1; i >= 0; i--){
if( c[p[i]] < 1 )
throw std::runtime_error("error");
b[--c[p[i]]] = p[i];
}
for(i = 0; i < length; i++)
p[i] = b[i];
delete [] c; c = NULL;
delete [] b; b = NULL;
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
countSort(a, 6, 60);
printArray(a, 6);
return 0;
}
运行结果为:
>> 2, 29, 30, 42, 50, 60,
2.6 基数排序
#include <iostream>
#include <stdexcept>
using namespace std;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
int getdigit(int x, int d){
int a[] = {1, 10, 100};
return (x/a[d]) % 10;
}
void radixSort(int *p, int length, int d, int radix){
if(p == NULL || length <= 0 || d <= 0)
throw std::runtime_error("NULL Pointer");
int i;
int *c = new int[radix+1];
int *b = new int[length];
for(int j = 0; j != d; j++){
for(i = 0; i < radix + 1; i++)
c[i] = 0;
for(i = 0; i < length; i++){
int r = getdigit(p[i], j);
if(r > radix)
throw std::runtime_error("invaild input");
c[r] += 1;
}
for(i = 1; i < radix + 1; i++)
c[i] += c[i-1];
for(i = length - 1; i >= 0; i--){
int r = getdigit(p[i], j);
if(c[r] < 1)
throw std::runtime_error("error");
b[--c[r]] = p[i];
}
for(i = 0; i < length; i++)
p[i] = b[i];
}
delete [] c; c = NULL;
delete [] b; b = NULL;
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
radixSort(a, 6, 2, 9);
printArray(a, 6);
return 0;
}
运行结果为:
>> 2, 29, 30, 42, 50, 60,
2.7 归并排序
#include <iostream>
#include <stdexcept>
using namespace std;
int INF = 0x7fffffff;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
void mergeCore(int *p1, int *p2, int p1Len, int p2Len){
if(p1 == NULL || p2 == NULL || p1Len <= 0 || p2Len <= 0)
throw std::runtime_error("error");
int *l = new int[p1Len+1];
int *r = new int[p2Len+1];
int i;
int m = 0;
int n = 0;
for(i = 0; i < p1Len; i++)
l[i] = p1[i];
l[i] = INF;
for(i = 0; i < p2Len; i++)
r[i] = p2[i];
r[i] = INF;
i = 0;
while(i < p1Len + p2Len){
if(r[n] < l[m]){
p1[i++] = r[n++];
}else{
p1[i++] = l[m++];
}
}
delete [] l; l = NULL;
delete [] r; r = NULL;
}
void mergeSort(int *p, int length){
if(p == NULL || length <= 0)
throw std::runtime_error("error");
if(length == 1)
return;
int llen,rlen;
llen = length >> 1;
rlen = length - llen;
mergeSort(p,llen);
mergeSort(p+llen,rlen);
mergeCore(p,p+llen,llen,rlen);
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
mergeSort(a, 6);
printArray(a, 6);
return 0;
}
运行结果为:
>> 2, 29, 30, 42, 50, 60,
2.8 快速排序
#include <iostream>
#include <stdexcept>
using namespace std;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
void quickSort(int *p, int length){
if(p == NULL || length <= 0)
throw std::runtime_error("error");
if(length == 1)
return;
int mid = 0;
int t;
for(int i = 0; i < length; i++){
if(p[i] < p[0]){
mid++;
t = p[mid]; p[mid] = p[i]; p[i] = t;
}
}
t = p[0]; p[0] = p[mid]; p[mid] = t;
int rlen = length - mid - 1;
if(mid > 0)
quickSort(p,mid);
if(rlen > 0)
quickSort(p+mid+1,rlen);
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
quickSort(a, 6);
printArray(a, 6);
return 0;
}
运行结果为:
>> 2, 29, 30, 42, 50, 60,
2.9 双向扫描的快速排序
#include <iostream>
#include <stdexcept>
using namespace std;
void printArray(int *p, int length) {
for (int i = 0; i < length; i++) {
cout << p[i] << ", ";
}
}
void quickSortDouble(int *p, int length){
if(p == NULL || length <= 0)
throw std::runtime_error("error");
if(length == 1)
return;
int i = 0;
int t;
int mid = length;
while(true){
do { i++; } while( i < length && p[i] < p[0]);
do { mid--; } while( mid > 0 && p[mid] > p[0] );
if(i > mid) break;
t = p[i]; p[i] = p[mid]; p[mid] = t;
}
t = p[0]; p[0] = p[mid]; p[mid] = t;
int rlen = length - mid - 1;
if(mid > 0)
quickSortDouble(p,mid);
if(rlen > 0)
quickSortDouble(p+mid+1,rlen);
}
int main()
{
int a[] = {30, 29, 50, 2, 42, 60};
quickSortDouble(a, 6);
printArray(a, 6);
return 0;
}
运行结果为:
>> 2, 29, 30, 42, 50, 60,
2.10 堆排序
/**
* @author lizejun
**/
public class HeapSort {
public static void heapSort() {
int[] arr = new int[]{9, 10, -1, 20, -30, 100};
int len = arr.length;
//1.初始化最大堆。
for (int i = len / 2 - 1; i >= 0; i--) {
heapAdjustNode(arr, i, len);
}
System.out.println(Arrays.toString(arr));
for (int i = len - 1; i >= 1; i--) {
//2.把最大的元素放到最后一个位置。
int temp = arr[0];
arr[0] = arr[i];
arr[i] = temp;
//3.维护堆的特性。
heapAdjustNode(arr, 0, i);
}
System.out.println(Arrays.toString(arr));
}
private static void heapAdjustNode(int[] arr, int i, int length) {
int temp = arr[i];
//2*i+1 表示的是父节点的左孩子节点。
for (int k = i * 2 + 1; k < length; k = 2 * k + 1) {
//1.获取左右子节点最大的值。
if (k + 1 < length && arr[k+1] > arr[k]) {
k++;
}
//2.1 如果左右孩子节点大于父节点,那么用它替代父节点。
if (arr[k] > temp) {
arr[i] = arr[k];
//上移的孩子节点作为下次循环的父节点。
i = k;
//2.2 反之说明满足最大堆的特性,跳出循环。
} else {
break;
}
}
arr[i] = temp;
}
}
运行结果为:
>> [100, 20, 9, 10, -30, -1]
>> [-30, -1, 9, 10, 20, 100]
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