[算法]将字符串中的*前置，非*字符相对位置不变

char* 
foo(char* str, int length){
    int i = length-1,j = length-1;
    while(i >= 0 && j >= 0){
        while(i >= 0 && ‘*‘ != str[i]){
            --i;
        }
        j = i - 1;
        while(j >= 0 && ‘*‘ == str[j]){
            --j;
        }
        if(j >= 0){
            char t = str[i];
            str[i] = str[j];
            str[j] = t;    
        }        
    }
    return str;
}