剑指offer：替换空格

class Solution {
public:
    void replaceSpace(char *str,int length) {
        int count = 0;  //计算空格的数量 
        for(int i = 0; i < length; i++){
            if(str[i] == ‘ ‘) count++;
        }
        if(count == 0 || length <= 0) return; //no space
        for(int i = length - 1; i >= 0; i--){
            if(str[i] != ‘ ‘) {
                str[i + 2*count] = str[i];
             }
            else{
                count--;  //每次替换都要减少count
                str[i + 2*count] = ‘%‘;
                str[i + 2*count + 1] = ‘2‘;
                str[i + 2*count + 2] = ‘0‘;
            }
        }
    }
};