Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:
 Input: "Let's take LeetCode contest"
 Output: "s'teL ekat edoCteeL tsetnoc" 

void reverse(int start,int end,char *s)
{
    char tmp;
    while(start < end)
    {
        tmp = s[start] ^ s[end];
        s[start] = tmp ^ s[start];
        s[end] = tmp ^ s[end];
        start++;
        end--;
    }
}

char* reverseWords(char* s) 
{
    int len = strlen(s);
    printf("%d\n",len);
    int index = 0;
    for(int i = 0;i <= len;i++)
    {
        if(s[i] == ' '|| s[i] =='\0')
        {
            reverse(index,i-1,s);
            index = i + 1;
        }
    }
    return s;
    
}

用到的交换两个整数的技巧 

tmp = a^b;
a = tmp ^a;
b = tmp ^a

另一个需要注意的地方是strlen的值与sizeof的值的关系，针对字符串，strlen(s) = sizeof(s) - 1;多的这个是'\0',一般我们的代码里都是< s.size()，这里比较特别，需要写成<= s.size(),然后再循环体重判断s[i] == 结束符这种场景。