java: add «916. Word Subsets»

URL:	https://leetcode.com/problems/word-subsets/
Signed-off-by: Matej Focko <me@mfocko.xyz>

java/word-subsets.java

@@ -9,14 +9,18 @@ class Solution {
     return freqs;
   }
 
-  private static boolean isUniversal(int[][] freqs2, String w) {
+  private static void merge(int[] cum, int[] freqs) {
+    for (var i = 0; i < 26; ++i) {
+      cum[i] = Math.max(cum[i], freqs[i]);
+    }
+  }
+
+  private static boolean isUniversal(int[] freqs2, String w) {
     var freqs = getFreqs(w);
 
-    for (var f : freqs2) {
-      for (var i = 0; i < 26; ++i) {
-        if (f[i] > freqs[i]) {
-          return false;
-        }
+    for (var i = 0; i < 26; ++i) {
+      if (freqs2[i] > freqs[i]) {
+        return false;
       }
     }
 
@@ -24,11 +28,12 @@ class Solution {
   }
 
   public List<String> wordSubsets(String[] words1, String[] words2) {
-    var freqs2 = new int[words2.length][];
+    var cumulativeFreqs = new int[26];
     for (var i = 0; i < words2.length; ++i) {
-      freqs2[i] = getFreqs(words2[i]);
+      var freqs = getFreqs(words2[i]);
+      merge(cumulativeFreqs, freqs);
     }
 
-    return Arrays.stream(words1).filter(w -> isUniversal(freqs2, w)).toList();
+    return Arrays.stream(words1).filter(w -> isUniversal(cumulativeFreqs, w)).toList();
   }
 }