字符流中第一个只出现一次的字符－C++

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// 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) { for (int i = 0; i < 256; ++i) occurrence[i] = -1; } void Insert(char ch) { if (occurrence[ch] == -1) occurrence[ch] = index; else if (occurrence[ch] >= 0) occurrence[ch] = -2; index++; } char FirstAppearingOnce() { char ch = '\0'; 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: // 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]; int index; }; // ====================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; } // ------ Output ------ /* Test1 begins: Passed. Test2 begins: Passed. Test3 begins: Passed. Test4 begins: Passed. Test5 begins: Passed. Test6 begins: Passed. Test7 begins: Passed. */