[NEW] #792 Number of Matching Subsequences

Author: Cappuccinuo

Array/792. Number of Matching Subsequences/README.md

@@ -0,0 +1,38 @@
+Time spent :  20 min(See hint)
+
+GIVEN: string S and a dictionary of words
+
+RETURNS: the number of words[i] that is a subsequence of S
+
+```
+Example :
+Input: 
+S = "abcde"
+words = ["a", "bb", "acd", "ace"]
+Output: 3
+Explanation: There are three words in words that are a subsequence of S: "a", "acd", "ace".
+```
+
+Algorithm:
+
+Put words into buckets by starting character. For words above
+
+we have head[0] : "a", "acd", "ace", head[1] : "bb"
+
+For each word, we create a class node, we have an index indicate the index of current node character, and the string word.
+
+1st: 
+
+"a", index = 1 == "a".length(), ans++
+
+"acd", index = 1 != "acd".length(), add "acd" to head[c - '0']
+
+"ace", index = 1 != "ace".length(), add "ace" to head[c - '0']
+
+2nd:
+
+"b", index = 1 != "bb".length(), add "bb" to head[b - '0']
+
+3rd:
+
+...

Array/792. Number of Matching Subsequences/Solution.java

@@ -0,0 +1,38 @@
+class Solution {
+    public int numMatchingSubseq(String S, String[] words) {
+        int result = 0;
+        List<Node>[] heads = new ArrayList[26];
+        for (int i = 0; i < 26; i++) {
+            heads[i] = new ArrayList<>();
+        }
+
+        for (String word : words) {
+            heads[word.charAt(0) - 'a'].add(new Node(word, 0));
+        }
+
+        for (char c : S.toCharArray()) {
+            List<Node> old_bucket = heads[c - 'a'];
+            heads[c - 'a'] = new ArrayList<>();
+            for (Node node : old_bucket) {
+                node.index++;
+                if (node.index == node.word.length()) {
+                    result++;
+                }
+                else {
+                    heads[node.word.charAt(node.index) - 'a'].add(node);
+                }
+            }
+            old_bucket.clear();
+        }
+        return result;
+    }
+}
+
+class Node {
+    String word;
+    int index;
+    public Node(String word, int index) {
+        this.word = word;
+        this.index = index;
+    }
+}

README.md

@@ -401,6 +401,7 @@
 | 397  | 859  |                     [Buddy Strings][859]                     |     Java     |    Easy    |       2018.6.24       |                     String                      |                                                              |
 | 398  | 856  |                 [Score of Parentheses][856]                  |     Java     |   Medium   |       2018.6.24       |                       DFS                       |                                                              |
 | 399  | 825  |              [Friends Of Appropriate Ages][825]              |     Java     |   Medium   |       2018.6.25       |                      Array                      |                                                              |
+| 400  | 792  |            [Number of Matching Subsequences][791]            |     Java     |   Medium   |       2018.6.26       |                      Array                      |                                                              |
 
 
 [1]:<https://leetcode.com/problems/two-sum/> "Two Sum"
@@ -785,6 +786,7 @@
 [781]:<https://leetcode.com/problems/rabbits-in-forest/> "Rabbits in Forest"
 [783]:<https://leetcode.com/problems/minimum-distance-between-bst-nodes/> "Minimum Distance between BST nodes"
 [784]:<https://leetcode.com/problems/letter-case-permutation/> "Letter Case Permutation"
+[792]:<https://leetcode.com/problems/number-of-matching-subsequences/> "Number of Matching Subsequences"
 [796]:<https://leetcode.com/problems/rotate-string/> "Rotate String"
 [801]:<https://leetcode.com/problems/minimum-swaps-to-make-sequences-increasing/> "Minimum Swaps to Makde Sequences Increasing"
 [813]:<https://leetcode.com/problems/largest-sum-of-averages/> "Largest Sum of Averages"