[LintCode] 空格替换

class Solution {
public:
    /**
     * @param string: An array of Char
     * @param length: The true length of the string
     * @return: The true length of new string
     */
    int replaceBlank(char string[], int length) {
        // Write your code here
        if (!length) return 0;
        int spaces = 0;
        for (int i = 0; string[i]; i++)
            if (string[i] == ' ')
                spaces++;
        if (!spaces) return length;
        int newlen = length + spaces * 2;
        int pn = newlen - 1, p = length - 1;
        while (p >= 0 && pn >= 0) {
            if (string[p] == ' ') {
                string[pn--] = '0';
                string[pn--] = '2';
                string[pn--] = '%';
                p--;
            }
            else string[pn--] = string[p--];
        }
        return newlen;
    }
};