[LeetCode] Excel Sheet Column Title、Excel Sheet Column Number

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** Excel Sheet Column Title

**

** Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

1 -> A

2 -> B

3 -> C

…

26 -> Z

27 -> AA

28 -> AB

**

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Note:

1、首先观察，其实这是个26进制的计数方式，它是从1开始计数，而不是0. （27 - 1 = 26， 类似于 10 -0 = 10）

2、存储顺序跟输出方式相反，字符数组需要反转；

void invertChar(char *pChar)  // 字符数组反转
{
char tmp;
int num = strlen(pChar) / sizeof(char);
char *pLeft, *pRight;

pLeft = pChar;
pRight = pChar + num - 1;

while(pLeft < pRight)
{
tmp = *pLeft;
*pLeft++ = *pRight;
*pRight-- = tmp;
}
}

char* convertToTitle(int n)  // 计数方式
{
int i = 0;
static char excelSh[10];

while (n)
{
excelSh[i++] = 'A' + (n - 1) % 26;
n = (n - 1) / 26;
}

excelSh[i] = '\0';
invertChar(excelSh);

return excelSh;
}

/[b]************[/b]

** Excel Sheet Column Number

**

** Given a column title as appear in an Excel sheet, return its corresponding column number.

For example:

1 -> A

2 -> B

3 -> C

…

26 -> Z

27 -> AA

28 -> AB

**

[b]***********[/b]/

Note：

1、跟上一题反过来，这是将数字转化为对应的字符序号，理解题目按26进制数排序。

int titleToNumber(char *s)
{
int i = 0;
int toNumber = 0;
int nums = strlen(s) / sizeof(char);

for (; i < nums; i++)  // 方法1
{
toNumber *= 26;
toNumber += s[i] - 'A' + 1;
}

return toNumber;
}