标签：class not found current open st3 === mini eve pass
// 面试题50（二）：字符流中第一个只出现一次的字符 // 题目：请实现一个函数用来找出字符流中第一个只出现一次的字符。例如，当从 // 字符流中只读出前两个字符"go"时，第一个只出现一次的字符是‘g‘。当从该字 // 符流中读出前六个字符"google"时，第一个只出现一次的字符是‘l‘。 #include <cstdio> #include <vector> #include <limits> using namespace std; class CharStatistics { public: CharStatistics() : index(0) //index=0时初始化hash表, 有点像构造函数 { for (int i = 0; i < 256; ++i) occurrence[i] = -1; } void Insert(char ch) //插入当前字符的位置到hash表中 { if (occurrence[ch] == -1) //未出现过 occurrence[ch] = index; else if (occurrence[ch] >= 0) //出现次数1次以上 occurrence[ch] = -2; ++index; } char FirstAppearingOnce() { char ch = ‘\0‘; int minIndex = numeric_limits<int>::max(); //类型int的最大值 for (int i = 0; i < 256; ++i) { //出现一次且位置最靠前的字符 if (occurrence[i] >= 0 && occurrence[i] < minIndex) { ch = (char)i; //转换为字符 minIndex = occurrence[i]; //更新最小位置 } } return ch; } private: // occurrence[i]: A character with ASCII value i; // occurrence[i] = -1: The character has not found; // occurrence[i] = -2: The character has been found for mutlple times // occurrence[i] >= 0: The character has been found only once int occurrence[256]; //hash表 int index; //当前字符流的位数 };
// ====================测试代码==================== void Test(const char* testName, CharStatistics chars, char expected) { if (testName != nullptr) printf("%s begins: ", testName); if (chars.FirstAppearingOnce() == expected) printf("Passed.\n"); else printf("FAILED.\n"); } int main(int argc, char* argv[]) { CharStatistics chars; Test("Test1", chars, ‘\0‘); chars.Insert(‘g‘); Test("Test2", chars, ‘g‘); chars.Insert(‘o‘); Test("Test3", chars, ‘g‘); chars.Insert(‘o‘); Test("Test4", chars, ‘g‘); chars.Insert(‘g‘); Test("Test5", chars, ‘\0‘); chars.Insert(‘l‘); Test("Test6", chars, ‘l‘); chars.Insert(‘e‘); Test("Test7", chars, ‘l‘); return 0; }
分析：哈希表在需要多次遍历字符串时真好用。
class Solution { public: Solution() : index(0) { for (int i = 0; i < 256; ++i) occurrence[i] = -1; } //Insert one char from stringstream void Insert(char ch) { if (occurrence[ch] == -1) occurrence[ch] = index; else if (occurrence[ch] >= 0) occurrence[ch] = -2; ++index; } //return the first appearence once char in current stringstream char FirstAppearingOnce() { char ch = ‘#‘; int minIndex = numeric_limits<int>::max(); for (int i = 0; i < 256; ++i) { if (occurrence[i] >= 0 && occurrence[i] < minIndex) { ch = (char)i; minIndex = occurrence[i]; } } return ch; } private: int occurrence[256]; int index; };
《剑指offer》第五十题II：字符流中第一个只出现一次的字符
标签：class not found current open st3 === mini eve pass
原文地址：https://www.cnblogs.com/ZSY-blog/p/12638459.html
