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count the words in a string
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// ====================== a good concise version ===================== 4/30/2014 == | |
// ================================================================================ | |
bool is_letter(char c) { return c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z'; } | |
int count_words(const string& s) { | |
int i = 0, N = s.size(), count = 0; | |
while(i < N) { | |
while(i < N && !is_letter(s[i])) i++; | |
if(i == N) break; | |
while(i < N && is_letter(s[i])) i++; | |
count++; | |
} | |
return count; | |
} | |
// ====================== a Divide-and-Conquer version ============== 4/30/2014 == | |
// =============================================================================== | |
int dc(const string& A, int low, int high) { | |
if(low > high) return 0; | |
int mid = low + (high - low) / 2; | |
int count_left = dc(A, low, mid-1); | |
int count_right = dc(A, mid+1, high); | |
if(!is_letter(A[mid])) | |
return count_left + count_right; | |
else { | |
if(mid == low && mid == high) return 1; | |
if(mid-1 < low) { | |
if(is_letter(A[mid+1])) return count_right; | |
else return count_right+1; | |
} else if(mid+1 > high) { | |
if(is_letter(A[mid-1])) return count_left; | |
else return count_left+1; | |
} | |
else { | |
if(!is_letter(A[mid-1]) && !is_letter(A[mid+1])) | |
return count_left + count_right + 1; | |
else if(is_letter(A[mid-1]) && is_letter(A[mid+1])) | |
return count_left + count_right - 1; | |
else | |
return count_left + count_right; | |
} | |
} | |
} | |
int count_words_divide_n_conquer(const string& s) { | |
return dc(s, 0, s.size()-1); | |
} | |
// ====================== a bad version ================================= | |
// ====================================================================== | |
bool is_letter(char c) { | |
return 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'; | |
} | |
int count_words(const char* s) { | |
if(!s || *s == '\0') return 0; | |
int count = 0, i = 0, len = strlen(s); | |
while(s[i] == ' ') i++; | |
if(i == len) return 0; | |
bool wordbegin = false; | |
while(i < len) { | |
if(is_letter(s[i])) { | |
if(!wordbegin) { | |
wordbegin = true; | |
count++; | |
} | |
i++; | |
} | |
else { | |
wordbegin = false; | |
while(s[i] == ' ' && i<len) i++; | |
} | |
} | |
return count; | |
} | |
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