Added string problems

strings/longest_common_substring.py

@@ -0,0 +1,33 @@
+def lcs(i, j):
+    if i == 0 or j == 0:
+        return 0
+    count = 0
+    if a[i-1] == b[j-1]:
+        return 1 + lcs(i-1, j-1)
+    else:
+        return max(count, lcs(i-1, j), lcs(i, j-1))
+
+
+def lcs_op(x, y, i, j):
+    answers = [[0 for columns in range(i+1)] for rows in range(j+1)]
+
+    result = 0
+
+    for m in range(i+1):
+        for n in range(j+1):
+            if m == 0 or n == 0:
+                answers[m][n] = 0
+            elif x[m-1] == y[n-1]:
+                answers[m][n] = 1 + answers[m-1][n-1]
+                result = max(result, answers[m][n])
+            else:
+                answers[m][n] = 0
+    return result
+
+a = "abcdxyz"
+b = "xyzabcd"
+m = len(a)
+n = len(b)
+x = lcs(m, n)
+x = lcs_op(a, b, m, n)
+print(x)

strings/lps.py

@@ -0,0 +1,34 @@
+def lps(a, i, j):
+    if not a:
+        return -1
+    if i == j:
+        return 1
+    if a[i] == a[j] and j == i+1:
+        return 2
+    if a[i] == a[j]:
+        return 2 + lps(a, i+1, j-1)
+    else:
+        return max(lps(a, i, j-1), lps(a, i+1, j))
+
+
+def lps_op(a):
+    n = len(a)
+    answers = [[0 for i in range(n)] for i in range(n)]
+    for i in range(n):
+        answers[i][i] = 1
+    for cl in range(2, n+1):
+        for i in range(n-cl+1):
+            j = i+cl-1
+            if a[i] == a[j] and cl == 2:
+                answers[i][j] = 2
+            elif a[i] == a[j]:
+                answers[i][j] = 2 + answers[i+1][j-1]
+            else:
+                answers[i][j] = max(answers[i][j-1], answers[i+1][j])
+    return answers[0][n-1]
+
+
+s = "GEEKSFORGEEKS"
+x = lps(s, 0, len(s)-1)
+x = lps_op(s)
+print(x)

strings/word_break_problem.py

@@ -0,0 +1,20 @@
+def word_found(a):
+    if not a:
+        return
+    i = 0
+    j = 1
+    found_words = []
+    while j <= len(a):
+        word = a[i:j]
+        if word in all_word:
+            found_words.append(word)
+            i = j
+            if j == len(a):
+                return found_words
+            continue
+        j += 1
+    return False
+
+all_word = ["i", "like", "sam", "sung", "samsung", "mobile", "ice", "cream", "icecream", "man", "go", "mango"]
+x = "ilikesam"
+print(word_found(x))