算法

参考书籍：《算法图解》《啊哈！算法》

1.二分查找 时间复杂度 log2(N)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace list
{
    class Program
    {
        //二分查找
        //数组必须有序
        public static int BinarySearch(List<int> intList, int target)
        {
            try
            {
                int? n = null;
                int low = 0;
                int high = intList.Count - 1;

                while (low <= high)
                {
                    int mid = (low + high) / 2;
                    if (intList[mid] == target)
                    {
                        Console.WriteLine("mid="+mid);
                        return mid;
                    }
                        
                    //low和high +-1是为了防止查找到边界时死循环
                    else if (intList[mid] > target)
                    {
                        high = mid-1;
                        Console.WriteLine("high=" + high + " mid="+mid);
                    }
                        
                    else
                    {
                        low = mid +1;
                        Console.WriteLine("low=" + low + " mid=" + mid);
                    }
                        
                }

                return n.Value;     //越界后跳转到catch{}
            }

            catch
            {
                int? n = null;
                Console.WriteLine("Error");
                return n.Value;     //返回null
            }
            
        }

        static void Main(string[] args)
        {
            int low = 1;
            int high = 9;

            List<int> list = new List<int>();
            for (int i = low; i < high; i++)
                list.Add(i);
            try
            {
                int a = BinarySearch(list, 10);
                int b = list[a];       //a值为null则跳转到catch{}
                Console.WriteLine("a.Index=" + a + " , a.Value= " + b);
            }

            catch
            {
                Console.WriteLine("Can't find target");
            }

            Console.ReadKey();
        }
    }
}

 2.选择排序

for (int j=0; j<array.Length-1;j++)
            {
                int min = j;
                int temp;
                for (int i = j; i < array.Length; i++)
                {
                    if (array[min] > array[i])
                    {
                        min = i;
                    }
                  
                }
                temp = array[min];
                array[min] = array[j];
                array[j] = temp;
            }

 3.冒泡排序

string str = Console.ReadLine();
            string[] strArray = str.Split(' ');
            int[] numArray = new int[strArray.Length];
            for(int i=0;i<strArray.Length;i++)
            {
                numArray[i] = Convert.ToInt32(strArray[i]);
            }
            for(int i=0;i<numArray.Length;i++)
            {
                for(int j=i+1;j<numArray.Length;j++)
                {
                    if(numArray[j]<numArray[i])
                    {
                        int temp = numArray[j];
                        numArray[j] = numArray[i];
                        numArray[i] = temp;
                    }
                }
            }

           for(int i=0;i<numArray.Length;i++)
            {
                Console.Write(numArray[i] + " ");
            }

            Console.ReadKey();

 

//当发生交换时继续排序，数组有序时则不交换
            int[] index = { 5, 4, 6 };
            bool isSwap = true;
            do
            {
                isSwap = false;
                for (int i = 0; i < index.Length - 1; i++)
                {
                    if (index[i] > index[i + 1])
                    {
                        int temp = index[i];
                        index[i] = index[i + 1];
                        index[i + 1] = temp;
                        isSwap = true;
                    }
                }
            } while (isSwap);

 

//类
    public class Employee
    {
        public string Name { get; private set; }
        public int Salary { get; private set; }

        public Employee(string name, int salary)
        {
            this.Name = name;
            this.Salary = salary;
        }

        //比较薪水大小
        public static bool Compare(Employee e1, Employee e2)
        {
            if (e1.Salary > e2.Salary)
                return true;

            return false;
        }
        //重写输出
        public override string ToString()
        {
            return Name + ":" + Salary;
        }
    }




/// <summary>
        /// 通用的冒泡排序方法
        /// </summary>
        /// <typeparam name="T">类型</typeparam>
        /// <param name="sortArray">数组</param>
        /// <param name="compareMethod">数组内置的比较方法，返回bool</param>
        static void CommonSort<T>(T[] sortArray,Func<T,T,bool> compareMethod)
        {
            bool isSwap = true;
            do
            {
                isSwap = false;
                for (int i = 0; i < sortArray.Length - 1; i++)
                {
                    if (compareMethod(sortArray[i],sortArray[i+1]))
                    {
                        T temp = sortArray[i];
                        sortArray[i] = sortArray[i + 1];
                        sortArray[i + 1] = temp;
                        isSwap = true;
                    }
                }
            } while (isSwap);
        }

 

4.乱序排序

int[] numArray = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
            int[] newArray = new int[numArray.Length];
            bool[] isAssigned = new bool[numArray.Length];  //判断是否已分配
            Random random = new Random();
            
            for(int i=0;i<numArray.Length;i++)
            {
                int n=0;
                bool isFounded= false;  //判断是否已找到
                while(isFounded==false)
                {
                    n = random.Next(numArray.Length);
                    if(isAssigned[n]==false)
                    {
                        isFounded = true;
                    }
                }
                isAssigned[n] = true;
                newArray[i] = numArray[n];
            }


            foreach(int n in newArray)
            {
                Console.Write(n + " ");
            }
            Console.ReadKey();

或者也可以设置成两个List<>,当生成随机数x后，把x从List中remove

 

5.快排 时间复杂度 n^2 ~ N*log2(N)

#include "pch.h"
#include <iostream>
#include <stdio.h>


int a[101], n;

void quickSort(int left, int right) {
    int i, j, t, temp;
    if (left > right) {
        return;
    }

    temp = a[left];
    i = left;
    j = right;
    while (i != j) {
        while (a[j] >= temp && i < j) {
            j--;
        }
        while (a[i] <= temp && i < j) {
            i++;
        }

        if (i < j) {
            t = a[i];
            a[i] = a[j];
            a[j] = t;
        }
    }

    a[left] = a[i];
    a[i] = temp;

    quickSort(left, i - 1);
    quickSort(i + 1, right);
    return;
}

int main()
{
    int i, j;
    scanf_s("%d", &n);
    for (i = 1; i <= n; ++i) {
        scanf_s("%d", &a[i]);
    }

    quickSort(1, n);

    for (i = 1; i <= n; ++i) {
        printf("%d", a[i]);
    }

    getchar();
    getchar();
    return 0;
}

 

6.队列

#include "pch.h"
#include <iostream>
#include <stdio.h>

struct queue 
{
    int data[101];
    int head;
    int tail;
};

int main()
{
    queue q;
    int i;
    q.head = 0;
    q.tail = 0;
    for (i = 0; i <= 8; i++) {
        scanf_s("%d", &q.data[q.tail]);
        q.tail++;
    }

    while (q.head<q.tail)
    {
        printf("%d", q.data[q.head]);
        q.head++;

        q.data[q.tail] = q.data[q.head];
        q.tail++;
        q.head++;
    }

    getchar();
    getchar();

    return 0;
}

 

7.栈 例判断是否为回文

#include "pch.h"
#include <iostream>
#include <stdio.h>
#include <string.h>

int main()
{
    char a[101], s[101];
    int i, len, mid, next, top;

    gets_s(a);
    len = strlen(a);
    mid = len / 2 - 1;

    top = 0;
    for (i = 0; i <= mid; ++i) {
        s[++top] = a[i];
    }

    if (len % 2 == 0) {
        next = mid + 1;
    }
    else
    {
        next = mid + 2;
    }

    for (i = next; i <= len - 1; ++i) {
        if (a[i] != s[top]) {
            break;
        }
        top--;
    }

    if (top == 0) {
        printf("YES");
    }
    else
    {
        printf("NO");
    }

    getchar();
    getchar();
    return 0;
}