From f6bc4fd4c62e42339080478bf8e12ebc42ceed74 Mon Sep 17 00:00:00 2001
From: WeiChungChang <r97922153@gmail.com>
Date: Mon, 22 Feb 2021 11:44:00 -0500
Subject: [PATCH] Merge pull request #19552 from WeiChungChang:partialSort

apply partial sort to save computations

* apply partial sort

* fix typo

* fix accroding to CR
---
 modules/dnn/src/layers/detection_output_layer.cpp | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/modules/dnn/src/layers/detection_output_layer.cpp b/modules/dnn/src/layers/detection_output_layer.cpp
index 76142181ae..55ef36f95c 100644
--- a/modules/dnn/src/layers/detection_output_layer.cpp
+++ b/modules/dnn/src/layers/detection_output_layer.cpp
@@ -611,8 +611,13 @@ public:
                 }
             }
             // Keep outputs k results per image.
-            std::sort(scoreIndexPairs.begin(), scoreIndexPairs.end(),
-                      util::SortScorePairDescend<std::pair<int, int> >);
+            if ((_keepTopK * 8) > scoreIndexPairs.size()) {
+                std::sort(scoreIndexPairs.begin(), scoreIndexPairs.end(),
+                          util::SortScorePairDescend<std::pair<int, int> >);
+            } else {
+                std::partial_sort(scoreIndexPairs.begin(), scoreIndexPairs.begin() + _keepTopK, scoreIndexPairs.end(),
+                          util::SortScorePairDescend<std::pair<int, int> >);
+            }
             scoreIndexPairs.resize(_keepTopK);
 
             std::map<int, std::vector<int> > newIndices;