excel表列序号#171

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28 
... 示例 1:

输入: "A"
输出: 1 示例 2:

输入: "AB"
输出: 28 示例 3:

输入: "ZY"
输出: 701

//C style
int heper(int x)
{
    if(x == 0) {
        return 1;
    }
    if(x <= 1) {
        return x*26;
    }
    return 26 * heper(x-1);
}

int titleToNumber(char* s) {
    int l = strlen(s);
    int sum = 0;
    for(int i = l - 1 ;i >= 0;i--) {

        int x =  (s[i] -'A' +1) *heper(l - i - 1);
        sum += x ;
    }

    return sum;
}

"ZY" 输出:

701