vault backup: 2022-09-06 13:15:36

OJ notes/pages/Leetcode Word-Pattern.md

@@ -61,6 +61,48 @@ Here **follow** means a full match, such that there is a bijection between a let
 > [!summary]
 > This is a #string operation problem.
 
+The main part is using two hash tables, to check for 
+mismatches, and using `istringstream` to read from string
 
+Two hash tables: 
+- One is used to check for s has one and only bound word
+- The other is used to check that the word is only stored 
+  once
+
+Using one hash table is one way, which makes one way 
+unchecked.
 
 ### Solution
+
+```cpp
+class Solution {
+public:
+  bool wordPattern(string pattern, string s) {
+    unordered_map<string, int> stoi;
+    unordered_map<char, int> ctoi;
+    // convert string to stream
+    istringstream input(s);
+    string word;
+    int n = pattern.size();
+    int id;
+
+    for (id = 0; input >> word; id++) {
+      // cout<<word<<'\n';
+      if (id == n || stoi[word] != ctoi[pattern[id]]) {
+        // pattern OOB, or mismatch.
+        return false;
+      }
+
+      // to prevent id == 0 is the default value of map
+      stoi[word] = ctoi[pattern[id]] = id + 1;
+    }
+
+    if (id == n) {
+      return true;
+    } else {
+      // check for lingering word in s
+      return false;
+    }
+  }
+};
+```