牛客网-《剑指offer》-替换空格

题目：http://www.nowcoder.com/practice/4060ac7e3e404ad1a894ef3e17650423

C++

class Solution {
public:
    void replaceSpace(char *str,int len) {
        int cnt = 0;
        for (int i = 0; i < len; i++) {
            if (str[i] == ' ') cnt++;
        }
        int idx = len + cnt * 2 - 1;
        for (int i = len - 1; i >= 0; i--) {
            if (str[i] == ' ') {
                str[idx--] = '0';
                str[idx--] = '2';
                str[idx--] = '%';
            } else {
                str[idx--] = str[i];
            }
        }
    }
};