091_ReverseWordsInSentence.cpp

// Coding Interviews: Questions, Analysis & Solutions
// Harry He

#include <stdio.h>
#include <string>

void Reverse(char *pBegin, char *pEnd) 
{
    if(pBegin == NULL || pEnd == NULL)
        return;

    while(pBegin < pEnd) 
    {
        char temp = *pBegin;
        *pBegin = *pEnd;
        *pEnd = temp;

        pBegin ++, pEnd --;
    }
}	

char* ReverseSentence(char *pData)
{
    if(pData == NULL)
        return NULL;

    char *pBegin = pData;

    char *pEnd = pData;
    while(*pEnd != '\0')
        pEnd ++;
    pEnd--;

    // Reverse the whole sentence
    Reverse(pBegin, pEnd);

    // Reverse every word in the sentence
    pBegin = pEnd = pData;
    while(*pBegin != '\0')
    {
        if(*pBegin == ' ')
        {
            pBegin ++;
            pEnd ++;
        }
        else if(*pEnd == ' ' || *pEnd == '\0')
        {
            Reverse(pBegin, --pEnd);
            pBegin = ++pEnd;
        }
        else
        {
            pEnd ++;
        }
    }

    return pData;
}

// ==================== Test Code ====================
void Test(char* testName, char* input, char* expectedResult)
{
    if(testName != NULL)
        printf("%s begins: ", testName);

    ReverseSentence(input);

    if((input == NULL && expectedResult == NULL)
        || (input != NULL && strcmp(input, expectedResult) == 0))
        printf("Passed.\n\n");
    else
        printf("Failed.\n\n");
}

// Multiple words
void Test1()
{
    char input[] = "I am a student.";
    char expected[] = "student. a am I";

    Test("Test1", input, expected);
}

// Only one word
void Test2()
{
    char input[] = "Wonderful";
    char expected[] = "Wonderful";

    Test("Test2", input, expected);
}

// Null pointer
void Test3()
{
    Test("Test3", NULL, NULL);
}

// empty string
void Test4()
{
    Test("Test4", "", "");
}

// Only blanks
void Test5()
{
    char input[] = "   ";
    char expected[] = "   ";
    Test("Test5", input, expected);
}

int main(int argc, char* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();

    return 0;
}