Pattern Searching algorithm

Author: hinagupta25sept

Pattern Searching Algo/brute force.py

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+#brute force for pattern searching .Time complexity O(m*(n-m+1))
+def search(pat, str): 
+    m = len(pat) 
+    n = len(str) 
+
+    for i in range(n-m+1):
+        j=0
+
+        for j in range(0, m):
+            if (str[i + j] != pat[j]):
+                break
+
+        if (j == m-1):
+            print("Pattern found at", i)
+
+if __name__ == '__main__':
+    str = "abcdabdadadcabdacabdac"
+    pat = "abda"
+    search(pat, str)
+

Pattern Searching Algo/kmpalgo.py

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+#effective approach for pattern searching KMP(Knuth Morris Pratt) algorithm.Time complexity O(n)
+def search(out, pat):
+    n=len(out)
+    m=len(pat)
+    #array for longest prefix suffix
+    p=[0]*m
+    compute(pat,m,p)
+    q = 0
+    i = 0
+    while i < n:
+        if pat[q]==out[i]:
+            q=q+1
+            i = i + 1
+        else:
+            if q != 0:
+                q = p[q-1]
+            else:
+                i = i + 1
+        if q == m:
+            print ("pattern occurs at "+str(i-q))
+            q = p[q-1]
+#function definition for preproscessing longest prefix suffix
+def compute(pat,m,p):
+   
+    k=1
+    l = 0
+    while k < m:
+        if pat[k] <= pat[l]:
+            l = l + 1
+            p[k] = l
+            k = k + 1
+        else:
+            if l != 0:
+                l = p[l-1]
+            else:
+                p[k] = 0
+                k = k + 1
+    
+#to find pattern from string out
+out = 'abcacdbacdabdacaabcdba'
+pat = 'dba'
+search(out,pat)