From feeba8243c375322f6efdda4ad3848061056f641 Mon Sep 17 00:00:00 2001
From: Longwei Liu <longwei.llw@gmail.com>
Date: Fri, 20 Feb 2026 19:04:05 +0800
Subject: [PATCH] chore(flat): replace std::map with std::unordered_map for
 key_id_mapping_

Reduces key lookup in get_id() from O(log N) to O(1) average, and index
load time from O(N log N) to O(N). Also lowers per-entry memory usage by
eliminating the three tree-node pointers (parent/left/right).
---
 src/core/algorithm/flat/flat_searcher.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/core/algorithm/flat/flat_searcher.h b/src/core/algorithm/flat/flat_searcher.h
index 78dcb1d3..207f38f5 100644
--- a/src/core/algorithm/flat/flat_searcher.h
+++ b/src/core/algorithm/flat/flat_searcher.h
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 #pragma once
-
+#include <unordered_map>
 #include <zvec/ailego/container/params.h>
 #include <zvec/core/framework/index_searcher.h>
 #include "flat_distance_matrix.h"
@@ -163,7 +163,7 @@ class FlatSearcher : public IndexSearcher {
  private:
   //! Members
   const uint64_t *keys_{nullptr};
-  std::map<key_t, node_id_t> key_id_mapping_;
+  std::unordered_map<key_t, node_id_t> key_id_mapping_;
   uint32_t magic_{IndexContext::GenerateMagic()};
   uint32_t read_block_size_{FLAT_DEFAULT_READ_BLOCK_SIZE};
   bool column_major_order_{false};