length N, for-O (M * N).
The code implementation is as follows:
int BF (const char *STR1, const char *str2)
{
int str1_len = strlen (str1);
int str2_len = strlen (str2);
int i = 0;
int j = 0;
if (str1 = null | | str2 = = NULL) {
return-1
}
while (I
The BF algorithm is easy to understand, but this algorithm is very inefficient, because every failure after backtracking, waste of previous comparisons, resulting in many times of useless comparisons, time loss
Algorithm-BM algorithm for String MatchingPreface
Boyer-Moore is a pattern string matching algorithm (BM) based on suffix matching. suffix matching means that pattern strings are compared from right to left, however, the mode string is still moved from left to right. In practice, the BM algorithm is more efficient than the KMP algorithm described earlier. The alg
The BM algorithm is a suffix-based algorithm. Therefore, it moves the mode string from left to right, while the comparison is from right to left.
The core of the BM algorithm is two parallel algorithms (good suffixes and bad characters). These two algorithms aim to move the pattern string as far as possible each time.
The definitions of good suffixes and bad characters are as follows:
The main string and m
First, briefly describe some basic concepts about the BM algorithm.
The BM algorithm is an exact string matching algorithm (different from fuzzy match ).
The BM algorithm uses the right-to-left comparison method and applies two heuristic rules, namely, the bad character rule and the suffix rule, to determine the distance to the right jump.
The basic process of th
Http://hi.baidu.com/l6834279/item/d6ef651684dda4fcddeecae3
First, briefly describe some basic concepts about the BM algorithm.
The BM algorithm is an exact string matching algorithm (different from fuzzy match ).
The BM algorithm uses the right-to-left comparison method and applies two heuristic rules, namely, the bad character rule and the suffix rule, to determ
The most famous two of the string lookup algorithms are the KMP algorithm Knuth-morris-pratt) and BM Algorithm (Boyer-moore). Two algorithms in the worst situationtime to find a linear search condition. The BM algorithm is often 3-5 times faster than the KMP algorithm. But the BM algorithm is not the fastest algorithm, here is a faster than the
The two most famous character string search algorithms are KMP algorithm (knuth-Morris-Pratt) and BM algorithm (Boyer-Moore). In the worst case, both algorithms have linear search time. However, in practice, the KMP algorithm is not much faster than the simplest C-database function strstr (), while the BM algorithm is usually 3-5 times faster than the KMP algorithm.
However, in the worst case, the time comp
1. KMP Algorithm
Code
Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->Def compute_prefix_function (p ):
M = len (p)
Pi = [0] * m
K = 0
For q in range (1, m ):
While k> 0 and p [k]! = P [q]:
K = pi [k-1]
If p [k] = p [q]:
K = k + 1
Pi [q] = k
Return pi
Def kmp_matcher (t, p ):N = len (t)M = len (p)Pi = compute_prefix_function (p)Q = 0For I in range (n ):While q> 0 and p [q]! = T [I]:Q = pi [q-1]If p [q] = t [I]:Q = q + 1If q = m:Return I-m + 1Re
The KMP match was matched from the beginning of the pattern string, and in 1977, Professor Robert S. Boyer of the University of Texas and Professor J Strother Moore invented a new string matching algorithm: Boyer-moore algorithm, or BM algorithm for short. The algorithm starts at the end of the pattern string and has a time complexity of O (N) in the worst case. In practice, the actual efficiency is higher than the KMP algorithm.The
=00000202kernel32!Loadlibraryw:7c80aeeb 8BFF mov edi,edi0: the>BL0E 7c80aeeb0001(0003)0:* * * * kernel32! LoadlibrarywWe notice that this breakpoint now shows 0001 (0003), which means that it was ignored two times before.The bu command is for a breakpoint under a symbol . Like Bu myapp!. SomeFunction. After the code has been modified, the breakpoint can be automatically updated to the latest position as the function address changes. And the BU breakpoint is saved in the Windbg workspace, and the
1. BM Algorithm Introduction:
KMP algorithm is not the most efficient string matching algorithm, the actual application is not much, the various text editor "find" function is mostly using BM algorithm (Boyer Moore). BM algorithm is more efficient and easier to understand.
2. BM Algorithm Analysis:
(1) Assuming that
Windbg debugging command 8 (BP, Bu, BM, BL, BC, Ba, Be, BD)
The following uses skinhgy as an example.
1.
BPThe command is inAn addressCan be BP 0x7783feb orBP MyApp! Somefunction.
For the latter, windbg will automatically find MyApp! The address corresponding to somefunction and the breakpoint. However, the problem with using BP is:
1) After the code is modified, the function address changes and the breakpoint remains in the same position, not necessa
Question:Given, there are three functions, H, B, A, and then t queries. Each time n is given, SQRT (an) is obtained );
Ideas:I don't know how to push it, but I feel that a should be linear. At this time, we can use BM linear recursion to find the first few items and put them in the template. Then we can find them.
The data range is 1e15, and 1000 groups can all be in seconds.
The main problem is to ensure that the data is linear and the first few item
BM
Algorithm Like the KMP algorithm, it also constructs an auxiliary pattern function to accelerate the matching speed. Compared with the KMP mode function, the BM mode function is simpler:
Void make_next (const char P [], int next []){For (INT I = 0; I Next [p [I] = I;}
Next [] is an array of 256 data records, which is the same as the ASCII number. Of course, if a duplicate character
Here is the code: BM is what reference Nanyi Teacher's explanation click Open link#include BM algorithm pattern Matching--comparison between string and KMP
The BM algorithm is an improvement of the KMP algorithm, which is 3-bit faster than the KMP algorithm ~ 5 times
The BM algorithm mainly follows two principles: 1. Bad characters, 2. Good suffixes.
Assume that the main string S exists. The length is s_l, and the pattern string T is t_l.
1. Bad characters
If there is a character in the main string S and this character does not exist in the mode string T, t
Recently, the algorithm has learned the HORSPOOL,KMP,BM three kinds of algorithms. Let's make a share.Horspool algorithm:Algorithm ideas: 1. Divided into matching strings, the original string2. Match from right to left: Once a mismatch is encountered, the original string moves table[i] characters relative to the matched string3.table[] by the original string each word Fusso to the original string each word typeface to match the string to the right of
The time complexity of the KMP algorithm is O (M + N), while the time complexity of the boyer-moore algorithm is O (n/m). In text lookup, "Ctrl + F" is generally used as the BM algorithm. key points of the Boyer-moore algorithm:from the right traversal, if there is a txt inside the i+j element and Pat inside the J element is inconsistent, adjusted. According to right[] adjustment, right[] similar to KMP algorithm inside the nextval. Skip = J-right[txt
performing the comparison.
Iii. BM algorithm
Compared with the KMP algorithm, the BM algorithm is more efficient. Unlike the general matching algorithm, In the BM algorithm, the pattern string is also moved from left to right, but the comparison process is indeed from right to left. The specific theoretical basis of the algorithm is as follows:
A. if yes, set
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