From c10e7bf42f8f117173e02e3799b1cc6727f1ff98 Mon Sep 17 00:00:00 2001
From: yennanliu <f339339@gmail.com>
Date: Sun, 8 Dec 2024 17:44:46 +0800
Subject: [PATCH] update cheatsheet, progress

---
 data/progress.txt          |  2 +-
 doc/cheatsheet/hash_map.md | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/data/progress.txt b/data/progress.txt
index eb66763c..ab8e2fbc 100644
--- a/data/progress.txt
+++ b/data/progress.txt
@@ -1,4 +1,4 @@
-20241208: 304,853,325
+20241208: 304,853,325,560(todo)
 20241202: 370(todo),1109(todo)
 20241130: 34,767
 20241126: 722,380
diff --git a/doc/cheatsheet/hash_map.md b/doc/cheatsheet/hash_map.md
index 63e55f16..21eb1c57 100644
--- a/doc/cheatsheet/hash_map.md
+++ b/doc/cheatsheet/hash_map.md
@@ -44,6 +44,17 @@
             - `TODO : note this as pattern!!!`
         - LC 325: Maximum Size Subarray Sum Equals k
             - `prefix sum` + hashmap
+        ```
+       subarray[i,j] = prefixSum[j] - prefixSum[i-1]
+
+       so, to find a subarray equals k
+
+       -> prefixSum[j] - prefixSum[i-1] = k
+
+       -> prefixSum[j]  - k = prefixSum[i-1]
+
+       -> so all need to do is : check if "prefixSum[j]  - k" is in map
+        ```
 - Any problems with below:
     - need to cache
     - avoid double loop