diff --git a/src/KTrie.cpp b/src/KTrie.cpp
index 5cd3a85b..4b12b307 100644
--- a/src/KTrie.cpp
+++ b/src/KTrie.cpp
@@ -17,7 +17,7 @@ namespace kiwi
 	{
 		static constexpr uint32_t npos = -1;
 
-		if (endPosMap[startPos].first == npos)
+		if (endPosMap[startPos].first == endPosMap[startPos].second)
 		{
 			return false;
 		}
@@ -30,15 +30,15 @@ namespace kiwi
 		nnode.prev = newId - endPosMap[startPos].first;
 		if (nnode.endPos >= endPosMap.size()) return true;
 
-		if (endPosMap[nnode.endPos].first == npos)
+		if (endPosMap[nnode.endPos].first == endPosMap[nnode.endPos].second)
 		{
 			endPosMap[nnode.endPos].first = newId;
-			endPosMap[nnode.endPos].second = newId;
+			endPosMap[nnode.endPos].second = newId + 1;
 		}
 		else
 		{
-			nodes[endPosMap[nnode.endPos].second].sibling = newId - endPosMap[nnode.endPos].second;
-			endPosMap[nnode.endPos].second = newId;
+			nodes[endPosMap[nnode.endPos].second - 1].sibling = newId - (endPosMap[nnode.endPos].second - 1);
+			endPosMap[nnode.endPos].second = newId + 1;
 		}
 		return true;
 	}
@@ -118,46 +118,34 @@ namespace kiwi
 		return true;
 	}
 
-	inline void removeUnconnected(Vector<KGraphNode>& ret, const Vector<KGraphNode>& graph)
+	inline void removeUnconnected(Vector<KGraphNode>& ret, const Vector<KGraphNode>& graph, const Vector<std::pair<uint32_t, uint32_t>>& endPosMap)
 	{
-		Vector<uint8_t> connectedList(graph.size());
-		Vector<uint16_t> newIndexDiff(graph.size());
-		connectedList[graph.size() - 1] = true;
-		connectedList[0] = true;
-		// forward searching
-		for (size_t i = 1; i < graph.size(); ++i)
-		{
-			bool connected = false;
-			for (auto prev = graph[i].getPrev(); prev; prev = prev->getSibling())
+		thread_local Vector<uint8_t> connectedList;
+		thread_local Vector<uint16_t> newIndexDiff;		
+		thread_local Deque<uint32_t> updateList;
+		connectedList.clear();
+		connectedList.resize(graph.size());
+		newIndexDiff.clear();
+		newIndexDiff.resize(graph.size());
+		updateList.clear();
+		updateList.emplace_back(graph.size() - 1);
+		connectedList[graph.size() - 1] = 1;
+
+		while (!updateList.empty())
+		{
+			const auto id = updateList.front();
+			updateList.pop_front();
+			const auto& node = graph[id];
+			const auto scanStart = endPosMap[node.startPos].first, scanEnd = endPosMap[node.startPos].second;
+			for (auto i = scanStart; i < scanEnd; ++i)
 			{
-				if (connectedList[prev - graph.data()])
-				{
-					connected = true;
-					break;
-				}
+				if (graph[i].endPos != node.startPos) continue;
+				if (connectedList[i]) continue;
+				updateList.emplace_back(i);
 			}
-			connectedList[i] = connected ? 1 : 0;
-		}
-		// backward searching
-		for (size_t i = graph.size() - 1; i-- > 1; )
-		{
-			bool connected = false;
-			for (size_t j = i + 1; j < graph.size(); ++j)
-			{
-				for (auto prev = graph[j].getPrev(); prev; prev = prev->getSibling())
-				{
-					if (prev > &graph[i]) break;
-					if (prev < &graph[i]) continue;
-					if (connectedList[j])
-					{
-						connected = true;
-						goto break_2;
-					}
-				}
-			}
-		break_2:
-			connectedList[i] = (connectedList[i] && connected) ? 1 : 0;
+			fill(connectedList.begin() + scanStart, connectedList.begin() + scanEnd, 1);
 		}
+
 		size_t connectedCnt = accumulate(connectedList.begin(), connectedList.end(), 0);
 		newIndexDiff[0] = connectedList[0];
 		for (size_t i = 1; i < graph.size(); ++i)
@@ -231,10 +219,15 @@ size_t kiwi::splitByTrie(
 	const PretokenizedSpanGroup::Span* pretokenizedLast
 )
 {
+	/*
+	* endPosMap[i]에는 out[x].endPos == i를 만족하는 첫번째 x(first)와 마지막 x + 1(second)가 들어 있다.
+	* first == second인 경우 endPos가 i인 노드가 없다는 것을 의미한다.
+	* first <= x && x < second인 out[x] 중에는 endPos가 i가 아닌 것도 있을 수 있으므로 주의해야 한다.
+	*/
 	thread_local Vector<pair<uint32_t, uint32_t>> endPosMap;
 	endPosMap.clear();
 	endPosMap.resize(str.size() + 1, make_pair<uint32_t, uint32_t>(-1, -1));
-	endPosMap[0] = make_pair(0, 0);
+	endPosMap[0] = make_pair(0, 1);
 	
 	thread_local Vector<uint32_t> nonSpaces;
 	nonSpaces.clear();
@@ -259,7 +252,8 @@ size_t kiwi::splitByTrie(
 			for (auto& cand : candidates)
 			{
 				const size_t nBegin = typoTolerant ? candTypoCostStarts[&cand - candidates.data()].start : (nonSpaces.size() - cand->sizeWithoutSpace());
-				const bool longestMatched = any_of(out.begin() + 1, out.end(), [&](const KGraphNode& g)
+				const auto scanStart = max(endPosMap[nBegin].first, (uint32_t)1), scanEnd = endPosMap[nBegin].second;
+				const bool longestMatched = scanStart < scanEnd && any_of(out.begin() + scanStart, out.begin() + scanEnd, [&](const KGraphNode& g)
 				{
 					return nBegin == g.endPos && lastSpecialEndPos == g.endPos - (g.uform.empty() ? g.form->sizeWithoutSpace() : g.uform.size());
 				});
@@ -335,7 +329,8 @@ size_t kiwi::splitByTrie(
 			}
 		}
 
-		bool duplicated = any_of(out.begin() + 1, out.end(), [&](const KGraphNode& g)
+		const auto scanStart = max(endPosMap[unkFormEndPos].first, (uint32_t)1), scanEnd = endPosMap[unkFormEndPos].second;
+		const bool duplicated = scanStart < scanEnd && any_of(out.begin() + scanStart, out.begin() + scanEnd, [&](const KGraphNode& g)
 		{
 			size_t startPos = g.endPos - (g.uform.empty() ? g.form->sizeWithoutSpace() : g.uform.size());
 			return startPos == lastSpecialEndPos && g.endPos == unkFormEndPos;
@@ -483,7 +478,8 @@ size_t kiwi::splitByTrie(
 			// sequence of speical characters found
 			if (lastChrType != POSTag::max && lastChrType != POSTag::unknown && lastChrType != lastMatchedPattern)
 			{
-				bool duplicated = any_of(out.begin() + 1, out.end(), [&](const KGraphNode& g)
+				const auto scanStart = max(endPosMap[nonSpaces.size()].first, (uint32_t)1), scanEnd = endPosMap[nonSpaces.size()].second;
+				const bool duplicated = scanStart < scanEnd && any_of(out.begin() + scanStart, out.begin() + scanEnd, [&](const KGraphNode& g)
 				{
 					return nonSpaces.size() == g.endPos;
 				});
@@ -514,6 +510,12 @@ size_t kiwi::splitByTrie(
 				break;
 			}
 		}
+		// 혹은 공백 문자가 아예 없는 경우 너무 길어지는 것을 방지하기 위해 강제로 중단
+		else if (n >= 8192)
+		{
+			lastChrType = chrType;
+			break;
+		}
 
 		// 공백문자를 무시하고 분할 진행
 		if (chrType == POSTag::unknown)
@@ -629,7 +631,8 @@ size_t kiwi::splitByTrie(
 	// sequence of speical characters found
 	if (lastChrType != POSTag::max && lastChrType != POSTag::unknown && !isWebTag(lastChrType))
 	{
-		bool duplicated = any_of(out.begin() + 1, out.end(), [&](const KGraphNode& g)
+		const auto scanStart = max(endPosMap[nonSpaces.size()].first, (uint32_t)1), scanEnd = endPosMap[nonSpaces.size()].second;
+		const bool duplicated = scanStart < scanEnd && any_of(out.begin() + scanStart, out.begin() + scanEnd, [&](const KGraphNode& g)
 		{
 			return nonSpaces.size() == g.endPos;
 		});
@@ -661,7 +664,7 @@ size_t kiwi::splitByTrie(
 
 	nonSpaces.emplace_back(n);
 
-	removeUnconnected(ret, out);
+	removeUnconnected(ret, out, endPosMap);
 	for (size_t i = 1; i < ret.size() - 1; ++i)
 	{
 		auto& r = ret[i];