20170928_替换空格

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20170928_替换空格
//面试题4//实现一个函数，将字符串中的每个空格都转换成"%20"。//例如："we are happy."//转换之后是："we20%are20%happy."//直观思路：从前至后，依次扫描字符串中的每个字符，遇到空格时就将其替换为"20%"，直到字符串结尾标识符'\0'。//时间复杂度是：O(n平方)//进阶思路：从后至前，使用两个指针，依次扫描字符串中的每个字符，遇到空格时就将其替换为"20%"，直到两个指针相等。//时间复杂度是：O(n)#include<iostream>#include<cstring>#include<string>#include<algorithm>using namespace std;class Solutions{public:void ReplaceBlank(char str[], int length)//length：代表字符数组的总长度{if(str==nullptr || length<=0)//输入的字符串是空，或者字符串长度是0return;int OriginalLen=0;int NumOfBlank=0;int i=0;while(str[i] != '\0'){++OriginalLen;if(str[i] == ' ')++NumOfBlank;++i;}int NewLen=0;NewLen=OriginalLen+NumOfBlank*2;if(NewLen>length)//字符数组溢出return;//cout<<OriginalLen<<","<<NumOfBlank<<","<<NewLen<<endl;//设置两个指针int p1=OriginalLen;//指向旧数组的末尾int p2=NewLen;//指向新数组的末尾while(p2 != p1){if(str[p1] == ' '){str[p2--]='0';str[p2--]='2';str[p2--]='%';--p1;}else{str[p2]=str[p1];--p1;--p2;}}}};int main(void){const int SIZE=50;char str[SIZE]="we are  happy.";//char str[SIZE]=" wearehappy.";//char str[SIZE]="wearehappy. ";//char str[SIZE]="wearehappy.";//char str[SIZE]="";cout<<str<<endl;Solutions object;object.ReplaceBlank(str,SIZE);cout<<str<<endl;system("pause");return 0;}
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