数据结构：字符串操作

字符串操作

字符串大小写转换
A-Z 65-90
a-z 97-122
n+32 = N

简便方法：使用位运算
A 100 0001
a 110 0001
大写字母二进制第六位始终为0，小写字母为1
按位与&：有0得0 小写转大写使用 &101 1111
按位或|：有1得1 大写转小写使用 |010 0000

demo.cpp

#include <stdio.h>
#include <stdlib.h>

/*
字符串拷贝
*/  
bool diyStrCpy(char *source, char *target,int len)
{
	//计算字符串总大小
	int i = 0;
	while (source[i] != '\0')
	{
		i++;
	}
	if (i > len)
	{
		return false;
	}

	//直接拷贝，无法判断字符串大小
	i = 0;
	while (source[i] != '\0')
	{
		target[i] = source[i];
		i++;
	}  
	target[i] = '\0';
	return true;
}  

/*
字符串连接
*/  
bool diyStrCat2(char *str1,int len, char *str2) //len代表str1内存总长度
{
	int i = 0;
	int k = 0;
	while (str2[k] != '/0')
	{
		k++;
	}
	while (str1[i] != '\0')
	{
		i++;
	}
	if (i + k -1 > len)
	{
		return false;
	}
	k = 0;
	while (str2[k] != '\0')
	{
		str1[i++] = str2[k++];
	}  
	str1[i] = '\0';  
	return true;

}  

/*
字符串连接
*/
bool diyStrCat3(char *str1, char *str2,char *target)
{
	int i = 0;
	int k = 0;
	
	//没有检验传入过来target是否有容纳两个字符串的空间
	while (str1[i] != '\0')
	{
		target[i] = str1[i];
		i++;
	}  
	while (str2[k] != '\0')
	{
		target[i++] = str2[k++];
	} 
	target[i] = '\0';
	return true;
}

大小写转换

常规方法

//大写字母转换为小写字母
bool diyStr2Low(char *str, char *target, int len)
{
	int strLen = 0; //字符串的长度，不带\0
	while (str[strLen] != '\0')
	{
		strLen++;
	}
	if (strLen >= len)
	{
		return false;
	}
	int k = 0;
	while (str[k] != '\0')
	{
		if (str[k] >= 'A'&& str[k] <= 'Z' )
		{
			target[k] = str[k] + 32;
			
		}
		else 
		{
			target[k] = str[k];
		}
		k++;
	}
	target[k] = '\0';
	return true;
}
//小写转大写
bool diyStr2High(char *str, char *target, int len)
{
	int strLen = 0; //字符串的长度，不带\0
	while (str[strLen] != '\0')
	{
		strLen++;
	}
	if (strLen >= len)
	{
		return false;
	}
	int k = 0;
	while (str[k] != '\0')
	{
		if (str[k] >= 'a'&& str[k] <= 'z')
		{
			target[k] = str[k] - 32;

		}
		else
		{
			target[k] = str[k];
		}
		k++;
	}
	target[k] = '\0';
	return true;
}

位运算

/*按位操作 大小写转换
前提条件：
1.target容量够存储转换后的内容
2.只有大小写字符，无其他字符  
*/
//大写转小写  按位或 0100 0000
bool diyStr2LowerEx(char *source, char *target)
{
	int k = 0;
	while (source[k] != '\0')
	{
		target[k] = source[k] | 32;
		k++;
	}
	target[k] = '\0';
	return true;
}
//小写转大写  按位与&  1011 1111
bool diyStr2UpperEx(char *source, char *target)
{
	int k = 0;
	while (source[k] != '\0')
	{
		target[k] = source[k] & 95;
		k++;
	}
	target[k] = '\0';
	return true;
}

字符串比较函数

bool diyStrCmp(char *str1, char *str2)
{
	//如果想不区分大小写，调用转换大小写函数后，再比较
	int k = 0;
	while (str1[k] != '\0')  //只要判断一个条件就可以了，因为另一个字符串到\0肯定会匹配失败退出
	{
		if (str1[k] != str2[k])
		{
			return false;
		}
		k++;
	}
	if (str1[k] == str2[k]) //都相等代表都到了结束位置
	{
		return true;
	}
	else
	{
		return false;
	}
}

字符串分割

demo.cpp

int diySeparateStr(char *source, char separator,char target[][20])
{
	int k = 0; //遍历用的索引
	int n = 0;  //要写入第几个字符串
	int i = 0;  //写入字符在当前字符串中的位置索引
	while (source[k] != '\0')
	{
		if (source[k] != separator)
		{
			target[n][i++] = source[k];
		}
		else
		{
			target[n][i] = '\0';
			n++;
			i = 0;
		}
		k++;
	}
	target[n][i] = '\0';
	return n+1;//返回子字符串的个数
}

查找算法

顺序查找，折半查找
折半查找：必须是有序集合

折半查找

//递归折半查找算法
int SearchAlg1(int *pArr, int target, int low, int high)
{
	int mid = 0;
	if (low > high)
	{
		return -1;
	}
	mid = (low + high) / 2;
	if (pArr[mid] == target)
	{
		return mid;
	}
	else if (pArr[mid] > target)
	{
		return SearchAlg1(pArr, target, low, mid - 1);
	}
	else if (pArr[mid] < target)
	{
		return SearchAlg1(pArr, target, mid + 1, high);
	}
}
//非递归折半查找算法
int SearchAlg2(int *pArr, int len,int target)
{
	int low = 0;
	int high = len - 1;
	int mid = (low + high) / 2;

	while (low < high && pArr[mid] != target)
	{
		if (pArr[mid] < target) //中间值小于目标值
		{
			low = mid + 1;
			mid = (low + high) / 2;
		}
		else if (pArr[mid] > target)
		{
			high = mid - 1;
			mid = (low + high) / 2;
		}
	}
	if (pArr[mid] == target)
	{
		return mid;
	}
	return -1;
}

猜商品价格

int GuessNum(int firstNum, int rightNum)
{
	//每次猜的价格都是上次价格的两倍
	int count = 1;
	int standardNum = firstNum;
	printf("standardNum = %d\n", standardNum);
	while (standardNum < rightNum)
	{
		count++;
		standardNum *= 2;
		printf("standardNum = %d\n", standardNum);
	}
	//找到比目标价格大的数（最靠近的）用折半查找
	int lowNum = 0;
	int highNum = standardNum;
	int midNum = highNum;
	while (midNum != rightNum)
	{
		if (midNum < rightNum)
		{
			lowNum = midNum;
			midNum = (lowNum + highNum) / 2;
		}
		else if(midNum > rightNum)
		{
			highNum = midNum;
			midNum = (lowNum + highNum) / 2;
		}
		printf("I guess %d\n", midNum);
		count++;
	}
	printf("ok\n");
	return count;
}