Create find-pattern-in-infinite-stream-ii.cpp

Author: kamyu104

C++/find-pattern-in-infinite-stream-ii.cpp

@@ -0,0 +1,40 @@
+// Time:  O(p + n)
+// Space: O(p)
+
+// kmp
+class Solution {
+public:
+    int findPattern(InfiniteStream* stream, vector<int>& pattern) {
+        const auto& getPrefix = [](const auto& pattern) {
+            vector<int> prefix(size(pattern), -1);
+            int j = -1;
+            for (int i = 1; i < size(pattern); ++i) {
+                while (j > -1 && pattern[j + 1] != pattern[i]) {
+                    j = prefix[j];
+                }
+                if (pattern[j + 1] == pattern[i]) {
+                    ++j;
+                }
+                prefix[i] = j;
+            }
+            return prefix;
+        };
+
+        vector<int> result;
+        const vector<int> prefix = getPrefix(pattern);
+        int j = -1;
+        for (int i = 0; ; ++i) {
+            const auto d = stream->next();
+            while (j > -1 && pattern[j + 1] != d) {
+                j = prefix[j];
+            }
+            if (pattern[j + 1] == d) {
+                ++j;
+            }
+            if (j == size(pattern) - 1) {
+                return i - j;
+            }
+        }
+        return -1;
+    }
+};