LeetCode #792: Number of Matching Subsequences

Author: ISKU

LeetCode/792/Solution.java

@@ -0,0 +1,57 @@
+/*
+ * Author: Minho Kim (ISKU)
+ * Date: November 8, 2019
+ * E-mail: minho.kim093@gmail.com
+ *
+ * https://github.com/ISKU/Algorithm
+ * https://leetcode.com/problems/number-of-matching-subsequences/
+ */
+
+class Solution {
+    
+    public int numMatchingSubseq(String S, String[] words) {
+        List<Integer>[] letters = new ArrayList[26];
+        for (int i = 0; i < 26; i++)
+            letters[i] = new ArrayList<Integer>() {{ add(-1); }};
+        for (int i = 0; i < S.length(); i++)
+            letters[S.charAt(i) - 'a'].add(i);
+        
+        int answer = 0;
+        for (String word : words) {
+            boolean contains = true;
+            int index = 0;
+            
+            for (int i = 0; i < word.length(); i++) {
+                List<Integer> indexes = letters[word.charAt(i) - 'a'];
+                int next = lowerBound(indexes, index);
+                if (next == -1) {
+                    contains = false;
+                    break;
+                }
+                
+                index = indexes.get(next) + 1;
+            }
+            
+            if (contains)
+                answer++;
+        }
+        
+        return answer;
+    }
+    
+    private int lowerBound(List<Integer> array, int target) {
+        int l = 0;
+        int r = array.size() - 1;
+        
+        while (l < r) {
+            int mid = (l + r) / 2;
+            
+            if (array.get(mid) < target)
+                l = mid + 1;
+            else
+                r = mid;
+        }
+        
+        return array.get(l) < target ? -1 : l;
+    }
+}