Language: C C++ D Haskell Lua OCaml PHP Perl Plain Text Python Ruby Scheme Tcl #include <stdio.h> #include <ctype.h> #include <limits.h> /// @brief Return first repeating character /// @param [in] s string to search for /// @ret '\0' If character not found /// @ret First repeating character (a-z, A-Z, 0-9) char findFirstRepeatingChar(const char *s) { char alreadyFound[1 << CHAR_BIT] = {0}; // I am using hashing data structure alreadyFound // to decrease the cost of algorithm to O(N). // Instead if I use std::set or a BST (Binary search tree) // cost will increase to O(N logN) while(*s != '\0') { // if( alreadyFound[*s] ) return s if( alreadyFound[*s] && isalnum(*s) ) return *s; alreadyFound[*s++] = 1; } return '\0'; } int main() { int testCaseNum; char testCases[][200] = { "This is a test.", "abcdefghi 1234 jklmnop 567890 zz", "abcdefghi 1234 jklmnop 567890 z", "", "abcabe", "a b c d should not output space", "x", "--", "aa" }; for(testCaseNum = 0; testCaseNum < 9; ++testCaseNum) { printf( "Input = %s\n", testCases[testCaseNum ] ); printf( "Output = %c\n" , findFirstRepeatingChar(testCases[testCaseNum ]) ); printf( "\n" ); } return 0; } Private [?] Run code Submit