From c2bdd92ec4b0afb6be43bf1610d19877ba397855 Mon Sep 17 00:00:00 2001
From: Jesse Millwood <dev@millwood.earth>
Date: Wed, 30 Oct 2024 17:49:58 -0400
Subject: [PATCH] Added sliding window

---
 Readme.org                       |  4 +-
 libs/chapter1/chapter1.hpp       |  2 +
 libs/chapter1/meson.build        |  3 +-
 libs/chapter1/sliding_window.cpp | 82 ++++++++++++++++++++++++++++++++
 tests/test.cpp                   | 14 ++++++
 5 files changed, 102 insertions(+), 3 deletions(-)
 create mode 100644 libs/chapter1/sliding_window.cpp

diff --git a/Readme.org b/Readme.org
index ce7a0c4..75857b1 100644
--- a/Readme.org
+++ b/Readme.org
@@ -44,13 +44,13 @@ To run the tests:
 #+end_src
 
 * Plan
-** Arrays [2/6]
+** Arrays [3/6]
 - [X] Is Unique (CTCI: 1.1)
 - [X] Check permutation (CTCI: 1.2)
 - [ ] String Compression (CTCI: 1.6)
 - [ ] Rotate Matrix (CTCI: 1.7)
 - [ ] Zero Matrix (CTCI: 1.8)
-- [ ] Sliding Window ([[https://www.geeksforgeeks.org/window-sliding-technique/][GfG: Sliding Window Technique]])
+- [X] Sliding Window ([[https://www.geeksforgeeks.org/window-sliding-technique/][GfG: Sliding Window Technique]])
 ** Linked Lists [1/6]
 - [X] Remove Duplicates (CTCI: 2.1)
 - [ ] Return Kth to Last (CTCI: 2.2)
diff --git a/libs/chapter1/chapter1.hpp b/libs/chapter1/chapter1.hpp
index ccc57c4..18fe0bb 100644
--- a/libs/chapter1/chapter1.hpp
+++ b/libs/chapter1/chapter1.hpp
@@ -4,3 +4,5 @@
 
 bool IsUnique(const char* s, int len);
 bool CheckPermutation(const char* s1, const char* s2, size_t s1_len, size_t s2_len);
+int sliding_window_max_sum(int* array, int len, int k_len);
+int sliding_window_shortest_subarray(int* array,int len, int x);
diff --git a/libs/chapter1/meson.build b/libs/chapter1/meson.build
index 490a549..a0fe21c 100644
--- a/libs/chapter1/meson.build
+++ b/libs/chapter1/meson.build
@@ -1,5 +1,6 @@
 
-chapter1_sources = ['is_unique.cpp', 'check_permutation.cpp']
+chapter1_sources = ['is_unique.cpp', 'check_permutation.cpp',
+                    'sliding_window.cpp']
 
 chapter1_lib = static_library('chapter1',
                               chapter1_sources)
diff --git a/libs/chapter1/sliding_window.cpp b/libs/chapter1/sliding_window.cpp
new file mode 100644
index 0000000..84dae79
--- /dev/null
+++ b/libs/chapter1/sliding_window.cpp
@@ -0,0 +1,82 @@
+#include "chapter1.hpp"
+
+/**
+ *  \brief sliding_window_max_sum
+ *
+ *  Detailed description
+ *
+ *  \param array The input array
+ *  \param len The length of the input array
+ *  \param k_len The length of the subarray
+ *  \return return int The maximum found in the subarray
+ */
+int sliding_window_max_sum(int* array, int len, int k_len){
+  int current_max = 0;
+  int* window_beg = array;
+  int* window_end = (array + k_len);
+  int previous_beg = 0;
+  // initial sum
+  for (int i = 0; i < k_len; i++){
+    current_max += array[i];
+  }
+  previous_beg = *window_beg;
+  window_beg += 1;
+  window_end += 1;
+
+  // iterate window
+  int current_sum = current_max;
+  while(window_end != (array + len - 1)){
+    current_sum = current_sum - previous_beg + *window_end;
+    if (current_sum > current_max){
+      current_max = current_sum;
+    }
+    previous_beg = *window_beg;
+    window_beg += 1;
+    window_end += 1;
+  }
+
+  return current_max;
+}
+
+
+/**
+ *  \brief sliding_window_shortest_subarray
+ *
+ *  Find the shortest subarray that is greater than or equal to x.
+ *
+ *  \param array The intput array
+ *  \param len The length of the input array
+ *  \param x The threshold to compare to
+ *  \return return the length of the shortest subarray
+ */
+int sliding_window_shortest_subarray(int* array,int len, int x){
+
+  int* window_beg = &array[0];
+  int* window_end = &array[1];
+  int current_sum = array[0] + array[1];
+  int min_len = len;
+  int sub_array_len = len;
+
+
+  while(window_beg != (array + len - 1)){
+    if(current_sum < x){
+      window_end += 1;
+      current_sum += *window_end;
+    }
+    if (current_sum >= x){
+      sub_array_len = window_end - window_beg + 1;
+      if(sub_array_len < min_len){
+        min_len = sub_array_len;
+      }
+      current_sum -= *window_beg;
+      window_beg += 1;
+      if(window_beg > window_end){
+        window_end += 1;
+        current_sum += *window_end;
+      }
+    }
+
+  }
+
+  return min_len;
+}
diff --git a/tests/test.cpp b/tests/test.cpp
index 1e47da6..092d6cb 100644
--- a/tests/test.cpp
+++ b/tests/test.cpp
@@ -32,6 +32,20 @@ TEST(ChapterOne, CheckPermutations){
 
 }
 
+TEST(ChapterOne, SubArraySum){
+  // Not actually in CTCI but is related to arrays
+
+  // Prompt: Given an array, find the sum of all subarrays of length K
+  // (fixed sliding window)
+  int a1[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+  CHECK_EQUAL(27, sliding_window_max_sum(a1, 11, 3));
+
+  // Prompt: Find the shortest subarray with a sum greater than or
+  // equal to X (dynamic sliding window)
+  int a2[] = {0, 1, 2, 3, 4, 5, 6, 7, 8};
+  CHECK_EQUAL(1, sliding_window_shortest_subarray(a2, 9, 7));
+}
+
 // Chapter 2: Linked Lists ___________________________________________
 
 TEST_GROUP(ChapterTwo){};