add kmp

README.md

@@ -84,6 +84,8 @@ Try to keep the interface and variable name consistent with the original book wh
   * [Quick3string](algs4/quick3_string.py)
   * [TrieST](algs4/trie_st.py)
   * [TST](algs4/tst.py)
+  * [KMP](algs4/kmp.py)
+
 ## License
 
 This code is released under MIT.

algs4/kmp.py

@@ -0,0 +1,71 @@
+"""
+ *  Execution:    python kmp.py pattern text
+ *
+ *  Reads in two strings, the pattern and the input text, and
+ *  searches for the pattern in the input text using the
+ *  KMP algorithm.
+ *
+ *  % python kmp.py abracadabra abacadabrabracabracadabrabrabracad
+ *  text:    abacadabrabracabracadabrabrabracad
+ *  pattern:               abracadabra
+ *
+ *  % python kmp.py rab abacadabrabracabracadabrabrabracad
+ *  text:    abacadabrabracabracadabrabrabracad
+ *  pattern:         rab
+ *
+ *  % python kmp.py bcara abacadabrabracabracadabrabrabracad
+ *  text:    abacadabrabracabracadabrabrabracad
+ *  pattern:                                   bcara
+ *
+ *  % python kmp.py rabrabracad abacadabrabracabracadabrabrabracad
+ *  text:    abacadabrabracabracadabrabrabracad
+ *  pattern:                        rabrabracad
+ *
+ *  % python kmp.py abacad abacadabrabracabracadabrabrabracad
+ *  text:    abacadabrabracabracadabrabrabracad
+ *  pattern: abacad
+ *
+"""
+
+
+class KMP:
+
+    def __init__(self, pattern):
+        self.pattern = pattern
+        self.R = 256
+        M = len(pattern)
+        self.dfa = [[0 for x in range(M)] for y in range(self.R)]
+        self.dfa[self.char_at(pattern, 0)][0] = 1
+        X = 0
+        for j in range(1, M):
+            for c in range(self.R):
+                self.dfa[c][j] = self.dfa[c][X]
+            self.dfa[self.char_at(pattern, j)][j] = j + 1
+            X = self.dfa[self.char_at(pattern, j)][X]
+
+    def search(self, txt):
+        N, M = len(txt), len(self.pattern)
+        i, j = 0, 0
+        while i < N and j < M:
+            j = self.dfa[self.char_at(txt, i)][j]
+            i += 1
+        # Found (hit end of pattern)
+            if j == M:
+                return i - M
+                # Not Found (hit end of text)
+        return N
+
+    def char_at(self, s, d):
+        return ord(s[d])
+
+
+if __name__ == "__main__":
+    import sys
+    pat, txt = sys.argv[1], sys.argv[2]
+    kmp = KMP(pat)
+    offset = kmp.search(txt)
+    print("text:    " + txt)
+    print("pattern: ", end="")
+    for i in range(offset):
+        print(" ", end="")
+    print(pat)

algs4/multiway.py

@@ -1,5 +1,5 @@
 """
-*  Compilation:  python multiway.py
+*  Execution:    python multiway.py
 *  Data files:   https://algs4.cs.princeton.edu/24pq/m1.txt
 *                https://algs4.cs.princeton.edu/24pq/m2.txt
 *                https://algs4.cs.princeton.edu/24pq/m3.txt