[LeetCode] Implement strStr()
代码：
暴力算法
1 class Solution { 2 public: 3 int strStr(char *haystack, char *needle) { 4 if (!*needle) 5 return 0; 6 int alen = strlen(haystack); 7 int blen = strlen(needle); 8 int i = 0, j = 0; 9 while (i < alen && j < blen) { 10 if (haystack[i] == needle[j]) { 11 i++; 12 j++; 13 } else { 14 i = i - j + 1; 15 j = 0; 16 } 17 } 18 if (j == blen) { 19 return i - j; 20 } else { 21 return -1; 22 } 23 } 24 };
KMP算法
1 class Solution { 2 public: 3 int strStr(char *haystack, char *needle) { 4 return kmp(haystack, needle); 5 } 6 private: 7 int kmp(const char *text, const char *pattern) { 8 int i = 0; 9 int j = 0; 10 const int n = strlen(text); 11 const int m = strlen(pattern); 12 int *next = (int*)malloc(sizeof(int)* m); 13 compute_prefix(pattern, next); 14 15 while (i < n && j < m) { 16 if (j == -1 || text[i] == pattern[j]) { 17 i++; 18 j++; 19 } else { 20 j = next[j]; 21 } 22 } 23 24 free(next); 25 if (j == m) 26 return i - j; 27 else 28 return -1; 29 } 30 31 void compute_prefix(const char *pattern, int next[]) { 32 int i = 0; 33 int j = -1; 34 const int m = strlen(pattern); 35 next[0] = -1; 36 37 while (i < m - 1) { 38 if (j == -1 || pattern[i] == pattern[j]) { 39 i++; 40 j++; 41 if (pattern[i] != pattern[j]) 42 next[i] = j; 43 else 44 next[i] = next[j]; 45 } 46 else { 47 j = next[j]; 48 } 49 } 50 } 51 };
杂记：
参考：http://blog.csdn.net/v_july_v/article/details/7041827
