added code of kmp algorithm in index.md (#22293)
* added code of kmp algorithm in index.md * format codeblock to c++? I think this is c++, but I'm not positive.pull/22333/head^2
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@ -53,6 +53,83 @@ How to use lps[] to decide next positions (or to know a number of characters to
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- From above two points, we can conclude that we do not need to match these lps[j-1] characters with txt[i-j…i-1] because we know that these characters will anyway match. Let us consider above example to understand this.
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<br>
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### Code Of KMP Algorithm in C++
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```cpp
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void computeLPSArray(char* pat, int M, int* lps)
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{
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// length of the previous longest prefix suffix
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int len = 0;
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lps[0] = 0; // lps[0] is always 0
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// the loop calculates lps[i] for i = 1 to M-1
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int i = 1;
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while (i < M) {
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if (pat[i] == pat[len]) {
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len++;
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lps[i] = len;
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i++;
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}
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else // (pat[i] != pat[len])
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{
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// This is tricky. Consider the example.
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// AAACAAAA and i = 7. The idea is similar
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// to search step.
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if (len != 0) {
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len = lps[len - 1];
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// Also, note that we do not increment
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// i here
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}
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else // if (len == 0)
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{
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lps[i] = 0;
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i++;
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}
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}
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}
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}
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```
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```cpp
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void KMPSearch(char* pat, char* txt)
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{
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int M = strlen(pat);
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int N = strlen(txt);
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// create lps[] that will hold the longest prefix suffix
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// values for pattern
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int lps[M];
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// Preprocess the pattern (calculate lps[] array)
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computeLPSArray(pat, M, lps);
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int i = 0; // index for txt[]
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int j = 0; // index for pat[]
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while (i < N) {
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if (pat[j] == txt[i]) {
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j++;
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i++;
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}
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if (j == M) {
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printf("Found pattern at index %d ", i - j);
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j = lps[j - 1];
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}
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// mismatch after j matches
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else if (i < N && pat[j] != txt[i]) {
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// Do not match lps[0..lps[j-1]] characters,
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// they will match anyway
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if (j != 0)
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j = lps[j - 1];
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else
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i = i + 1;
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}
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}
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}
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```
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**More Infromation :**
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- [kmp algorithm for pattern searching](https://www.geeksforgeeks.org/kmp-algorithm-for-pattern-searching/)
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- [Knuth–Morris–Pratt algorithm](https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm)
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- [Knuth–Morris–Pratt algorithm](https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm)
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