C++字串空格替換題

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在網路編程中，需要將URL參數中含有的特殊字元通過在‘%‘後加上ASCII碼的兩位十六進位的方法，轉換成伺服器端能夠識別的字元，如空格的ASCII碼為32即16進位的0x20，則需要替換為"%20"。

題目：請實現一個函數，把傳入char*字串中的每個空格替換成"%20"，例如輸入"We are happy."，則輸出"We%20are%20happy."

 

時間複雜度為O(n)的解法思路：

首先遍曆字串，得到字串長度originalLength並統計空格數numberOfBlank，可計算出替換後的字串長度newLength = originalLength+2*numberOfBlank；

從字串的尾部開始複製並向前移動，用兩個下標IndexOfOriginal和IndexOfNew分別標記目前所指的原字元位置和替換後的字元位置；

當IndexOfOriginal指向空格時，IndexOfNew下標所指的字元及其往前1、2個位置分別替換為‘0‘、‘2‘、‘%‘，替換完成後IndexOfOriginal向前移動一格，IndexOfNew相應向前移動3格，否則都往前移動一格；

最後在字串尾部即下標為newLength-1的位置添加‘\0‘。

 

代碼：

 

void ReplaceBlank(char str[], int maxLength) {    if(str == NULL || maxLength <=0)        return;        //calculate the new length after replacing and number of Blanks    int originalLength = 0;    int numberOfBlank = 0;    int index = 0;    for(index = 0; str[index] != ‘\0‘; index++) {        if(str[index] == ‘ ‘)            ++numberOfBlank;    }    originalLength = index+1;        //if the number of blank is 0, nothing changes    if(numberOfBlank==0)        return;        //if the new length exceeds the max length    int newLength = originalLength+2*numberOfBlank;    if (newLength > maxLength) {        cout << "new Length exceeds the max Length!" << endl;        return;    }    //start at the character before ‘\0‘    int indexOfOriginal = originalLength-2;    int indexOfNew = newLength-2;    while (indexOfOriginal>=0 && indexOfNew > indexOfOriginal) {        if (str[indexOfOriginal] == ‘ ‘) {            str[indexOfNew--] = ‘0‘;            str[indexOfNew--] = ‘2‘;            str[indexOfNew--] = ‘%‘;        } else {            str[indexOfNew--] = str[indexOfOriginal];        }        --indexOfOriginal;    }    //add a ‘\0‘ at last    str[newLength-1] = ‘\0‘;}

 

 

完整代碼：

#include <iostream>#include <stdio.h>using namespace std;void ReplaceBlank(char str[], int maxLength) {    if(str == NULL || maxLength <=0)        return;        //calculate the new length after replacing and number of Blanks    int originalLength = 0;    int numberOfBlank = 0;    int index = 0;    for(index = 0; str[index] != ‘\0‘; index++) {        if(str[index] == ‘ ‘)            ++numberOfBlank;    }    originalLength = index+1;        //if the number of blank is 0, nothing changes    if(numberOfBlank==0)        return;        //if the new length exceeds the max length    int newLength = originalLength+2*numberOfBlank;    if (newLength > maxLength) {        cout << "new Length exceeds the max Length!" << endl;        return;    }    //start at the character before ‘\0‘    int indexOfOriginal = originalLength-2;    int indexOfNew = newLength-2;    while (indexOfOriginal>=0 && indexOfNew > indexOfOriginal) {        if (str[indexOfOriginal] == ‘ ‘) {            str[indexOfNew--] = ‘0‘;            str[indexOfNew--] = ‘2‘;            str[indexOfNew--] = ‘%‘;        } else {            str[indexOfNew--] = str[indexOfOriginal];        }        --indexOfOriginal;    }    //add a ‘\0‘ at last    str[newLength-1] = ‘\0‘;}void test(char str[], int maxLength) {    cout << "-----------test-------------" << endl;    printf("Original: %s\n", str);    ReplaceBlank(str, maxLength);    printf("Replaced: %s\n", str);    cout << "-----------end---------------" << endl;    }int main() {    /*    char str[50] = "hello world and s";    ReplaceBlank(str, 50);    printf("%s\n", str);     */    char str1[50]="hello world and s";    char str2[50]="";    char str3[20]="hello world! fdsjkd";    char str4[50]="    helloweroddfsd";    char str5[50]="       ";    test(str1, 50);    test(str2, 50);    test (NULL, 50);    test(str3, 20);    test(str4, 50);    test(str5, 50);    return 0;}

 

參考資料：《劍指Offer名企面試官精講典型編程題》 

C++字串空格替換題