Prob 181: Word pattern problem

README.md

@@ -6,7 +6,7 @@
 
 | Current Status|     Stats     |
 | :------------: | :----------: |
-| Total Problems | 180 |
+| Total Problems | 181 |
 
 </center>
 
@@ -257,3 +257,8 @@ Include contains single header implementation of data structures and some algori
 | Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results. Note: The input string may contain letters other than the parentheses ( and ) | [remove_invalid_parenthesis.cpp](leet_code_problems/remove_invalid_parenthesis.cpp)|
 | Given an array and a value, remove all instances of that value in-place and return the new length. Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory. The order of elements can be changed. It doesn't matter what you leave beyond the new length.| [remove_element.cpp](leet_code_problems/remove_element.cpp)|
 | Find intersection of two arrays/vectors, Given two vectors find the result of their interaction. The result should only contain unique characters and can be in any order|[intersection_of_array.cpp](leet_code_problems/intersection_of_array.cpp)|
+| Given a pattern and a string str, find if str follows the same pattern. Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str. example:
+pattern = "abba", str = "dog cat cat dog" should return true.
+pattern = "abba", str = "dog cat cat fish" should return false.
+pattern = "aaaa", str = "dog cat cat dog" should return false.
+pattern = "abba", str = "dog dog dog dog" should return false.| [word_pattern.cpp](leet_code_problems/word_pattern.cpp)|

leet_code_problems/word_pattern.cpp

@@ -0,0 +1,76 @@
+/*
+ *
+ * Given a pattern and a string str, find if str follows the same pattern.
+ * Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str.
+ * Examples:
+ * pattern = "abba", str = "dog cat cat dog" should return true.
+ * pattern = "abba", str = "dog cat cat fish" should return false.
+ * pattern = "aaaa", str = "dog cat cat dog" should return false.
+ * pattern = "abba", str = "dog dog dog dog" should return false.
+ * Notes:
+ * You may assume pattern contains only lowercase letters, and str 
+ * contains lowercase letters separated by a single space.
+ * 
+ * Approach:
+ * 
+ * Split the string into words, and then map it to each character of the patterns as _we move.
+ * If the character is being mapped to multiple words, or a word is being mapped to multiple
+ * character, then the str is not following pattern.
+ */
+
+#include <iostream>
+#include <vector>
+#include <sstream>
+#include <unordered_map>
+#include <unordered_set>
+
+bool match_pattern(const std::string& str, const std::string& pattern)
+{
+    // split string to words
+    std::istringstream iss(str);
+    std::vector<std::string> words(std::istream_iterator<std::string>{iss}, 
+                                std::istream_iterator<std::string>());
+    if (words.size() != pattern.size()) {
+        return false;
+    }
+
+    std::unordered_map<char, std::string> map;
+    std::unordered_set<std::string> set;
+    for (int i = 0; i < pattern.size(); ++i) {
+        if (map.find(pattern[i]) != map.end()) {
+            // pattern is already mapped to some other string.
+            if (words[i] != map[pattern[i]]) {
+                return false;
+            }
+        } else {
+            // word is already mapped to some other string.
+            if (set.count(words[i])) {
+                return false;
+            } else {
+                map[pattern[i]] = words[i];
+                set.insert(words[i]);
+            }
+        }
+    }
+    return true;
+}
+
+int main() {
+    std::string pattern{"abba"};
+    std::string str{"dog cat cat dog"};
+    std::cout << "Pattern : " << pattern << std::endl;
+    std::cout << "String :" << str << std::endl;
+    bool r = match_pattern(str, pattern);
+    std::string result = (r) ? "true" : "false";
+    std::cout << "Result :" << result << std::endl;
+
+    pattern = "aaaa";
+    std::cout << "Pattern : " << pattern << std::endl;
+    std::cout << "String :" << str << std::endl;
+    r = match_pattern(str, pattern);
+    result = (r) ? "true" : "false";
+    std::cout << "Result :" << result << std::endl;
+
+
+    return 0;
+}