翻轉句子中單詞順序

題目描述：

<div class="line number2 index1 alt1" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; color: rgb(57, 57, 57); margin: 0px !important; padding: 0px 1em 0px 0px !important; border-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 1.8em !important; outline: 0px !important; overflow: visible !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="cpp comments" style="white-space: pre-wrap; margin: 0px !important; padding: 0px !important; border-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 1.8em !important; outline: 0px !important; overflow: visible !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; min-height: inherit !important; color: rgb(0, 130, 0) !important; background: none !important;">題目描述：翻轉句子中單詞的順序，但單詞內字符的順序不變。句子中單詞以空格符隔開。</code></div><div class="line number3 index2 alt2" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; color: rgb(57, 57, 57); margin: 0px !important; padding: 0px 1em 0px 0px !important; border-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 1.8em !important; outline: 0px !important; overflow: visible !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; background: none rgb(244, 244, 244) !important;"><code class="cpp comments" style="white-space: pre-wrap; margin: 0px !important; padding: 0px !important; border-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 1.8em !important; outline: 0px !important; overflow: visible !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; min-height: inherit !important; color: rgb(0, 130, 0) !important; background: none !important;">爲簡單起見，標點符號和普通字母一樣處理。如："I am a student."翻轉成"student. a am I"。</code></div>

具體算法C++實現如下：

#include<iostream>
#include<vector>
#include<assert.h>
#include<cstring>
using namespace std;
 
void swap(char &a, char &b)
{
    char tmp = b;
    b = a;
    a = tmp;
}
 
void swap_str(char* str, int start, int end)
{
    assert(str!=NULL && start <= end);
    int low = start;
    int high = end;
 
    //整個句子按字符翻轉
    while (low < high)
    {
        swap(str[low], str[high]);
        low++;
        high--;
    }
 
}
 
//方法一：依次讀入句子中的每個單詞，並將它們放入一個棧中。然後再將單詞出棧。
//時間複雜度：O(n)，空間複雜度:O(n)；
 
//方法二：首先將整個句子按字符翻轉，然後再將其中每個單詞的字符旋轉。
//時間複雜度：O(n)，空間複雜度:O(1)；
void reverse_word(char str[])
{
    int len = strlen(str);
 
    //翻轉整個句子
    swap_str(str, 0, len-1);
 
    int s = 0;
    int e = 0;
    //翻轉每個單詞
    for (int i=0; i<len; i++)
    {
        e = i;
        if (str[e] == ' ')
        {
            //str[e]爲空格，所以範圍是[s,e-1].
            swap_str(str, s, e-1);
            s = e + 1;
        }
    }
}
 
int main()
{
    char str[] = "I am a student.";
    reverse_word(str);
    cout<<str<<endl;
    return 0;
}