From 4213391fc439ce9f4790e30d096f03e74939b636 Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Sun, 29 Dec 2024 14:04:02 +0900
Subject: [PATCH 01/10] feat: 21. Merge Two Sorted Lists

---
 merge-two-sorted-lists/gwbaik9717.js | 46 ++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 merge-two-sorted-lists/gwbaik9717.js

diff --git a/merge-two-sorted-lists/gwbaik9717.js b/merge-two-sorted-lists/gwbaik9717.js
new file mode 100644
index 000000000..513778a83
--- /dev/null
+++ b/merge-two-sorted-lists/gwbaik9717.js
@@ -0,0 +1,46 @@
+// m: list1, n: list2
+// Time complexity: O(m+n)
+// Space complexity: O(m+n)
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} list1
+ * @param {ListNode} list2
+ * @return {ListNode}
+ */
+var mergeTwoLists = function (list1, list2) {
+  const answer = new ListNode();
+  let current = answer;
+
+  while (list1 && list2) {
+    if (list1.val < list2.val) {
+      current.next = new ListNode(list1.val);
+      list1 = list1.next;
+    } else {
+      current.next = new ListNode(list2.val);
+      list2 = list2.next;
+    }
+
+    current = current.next;
+  }
+
+  while (list1) {
+    current.next = new ListNode(list1.val);
+    list1 = list1.next;
+    current = current.next;
+  }
+
+  while (list2) {
+    current.next = new ListNode(list2.val);
+    list2 = list2.next;
+    current = current.next;
+  }
+
+  return answer.next;
+};

From e97aff4859fff20938b46fb1c8a31e39922be7df Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Mon, 30 Dec 2024 08:03:38 +0900
Subject: [PATCH 02/10] feat: 268. Missing Number

---
 missing-number/gwbaik9717.js | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 missing-number/gwbaik9717.js

diff --git a/missing-number/gwbaik9717.js b/missing-number/gwbaik9717.js
new file mode 100644
index 000000000..5df34e02c
--- /dev/null
+++ b/missing-number/gwbaik9717.js
@@ -0,0 +1,15 @@
+// Time complexity: O(n)
+// Space complexity: O(1)
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var missingNumber = function (nums) {
+  const n = nums.length;
+  const target = (n * (n + 1)) / 2;
+
+  const sum = nums.reduce((a, c) => a + c, 0);
+
+  return target - sum;
+};

From 43853fcc2ea1758dfd57c1a9e03fcde02e73ee90 Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Mon, 30 Dec 2024 08:53:55 +0900
Subject: [PATCH 03/10] feat: 79. Word Search

---
 word-search/gwbaik9717.js | 62 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 word-search/gwbaik9717.js

diff --git a/word-search/gwbaik9717.js b/word-search/gwbaik9717.js
new file mode 100644
index 000000000..182641028
--- /dev/null
+++ b/word-search/gwbaik9717.js
@@ -0,0 +1,62 @@
+// h: height of the board, w: width of the board, n: length of the word
+// Time complexity: O(h * w * 4**n)
+// Space complexity: O(h * w + n)
+
+/**
+ * @param {character[][]} board
+ * @param {string} word
+ * @return {boolean}
+ */
+var exist = function (board, word) {
+  const n = word.length;
+  const h = board.length;
+  const w = board[0].length;
+
+  const dy = [1, 0, -1, 0];
+  const dx = [0, 1, 0, -1];
+
+  const checked = Array.from({ length: h }, () =>
+    Array.from({ length: w }, () => 0)
+  );
+
+  let answer = false;
+
+  const dfs = (current, index) => {
+    if (index === n - 1) {
+      answer = true;
+      return;
+    }
+
+    const [cy, cx] = current;
+    checked[cy][cx] = 1;
+
+    for (let i = 0; i < dy.length; i++) {
+      const ny = cy + dy[i];
+      const nx = cx + dx[i];
+      const ni = index + 1;
+
+      if (
+        ny >= 0 &&
+        ny < h &&
+        nx >= 0 &&
+        nx < w &&
+        checked[ny][nx] === 0 &&
+        word[ni] === board[ny][nx]
+      ) {
+        dfs([ny, nx], ni);
+      }
+    }
+
+    checked[cy][cx] = 0;
+  };
+
+  for (let i = 0; i < h; i++) {
+    for (let j = 0; j < w; j++) {
+      if (board[i][j] === word[0] && !answer) {
+        dfs([i, j], 0);
+      }
+    }
+  }
+
+  return answer;
+};

From 32c4b5660ac831414aab9acf62bb63d4a4f0f33a Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Wed, 1 Jan 2025 10:09:09 +0900
Subject: [PATCH 04/10] feat: 647. Palindromic Substrings

---
 palindromic-substrings/gwbaik9717.js | 46 ++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 palindromic-substrings/gwbaik9717.js

diff --git a/palindromic-substrings/gwbaik9717.js b/palindromic-substrings/gwbaik9717.js
new file mode 100644
index 000000000..6d65d5e8b
--- /dev/null
+++ b/palindromic-substrings/gwbaik9717.js
@@ -0,0 +1,46 @@
+// Time complexity: O(n^2)
+// Space complexity: O(n^2)
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var countSubstrings = function (s) {
+  const n = s.length;
+  const dp = Array.from({ length: n }, () =>
+    Array.from({ length: n }, () => false)
+  );
+
+  for (let end = 0; end < n; end++) {
+    for (let start = end; start >= 0; start--) {
+      if (start === end) {
+        dp[start][end] = true;
+        continue;
+      }
+
+      if (start + 1 === end) {
+        if (s[start] === s[end]) {
+          dp[start][end] = true;
+        }
+        continue;
+      }
+
+      if (s[start] === s[end] && dp[start + 1][end - 1]) {
+        dp[start][end] = true;
+        continue;
+      }
+    }
+  }
+
+  let answer = 0;
+
+  for (let i = 0; i < n; i++) {
+    for (let j = 0; j < n; j++) {
+      if (dp[i][j]) {
+        answer++;
+      }
+    }
+  }
+
+  return answer;
+};

From ca72dd45ac485eb182f47ceb1b725edbb49265d2 Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Wed, 1 Jan 2025 11:47:56 +0900
Subject: [PATCH 05/10] feat: 322. Coin Change

---
 coin-change/gwbaik9717.js | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 coin-change/gwbaik9717.js

diff --git a/coin-change/gwbaik9717.js b/coin-change/gwbaik9717.js
new file mode 100644
index 000000000..e2b0b78a2
--- /dev/null
+++ b/coin-change/gwbaik9717.js
@@ -0,0 +1,33 @@
+// n: amount m: length of coins
+// Time complexity: O(n * m) + O(mlogm)
+// Space complexity: O(n * m)
+
+/**
+ * @param {number[]} coins
+ * @param {number} amount
+ * @return {number}
+ */
+var coinChange = function (coins, amount) {
+  const dp = Array.from({ length: coins.length + 1 }, () =>
+    Array.from({ length: amount + 1 }, () => Infinity)
+  );
+  coins.sort((a, b) => a - b);
+
+  for (let i = 0; i < coins.length + 1; i++) {
+    dp[i][0] = 0;
+  }
+
+  for (let i = 1; i <= amount; i++) {
+    for (let j = 1; j <= coins.length; j++) {
+      const coin = coins[j - 1];
+
+      if (i >= coin) {
+        dp[j][i] = Math.min(dp[j][i], 1 + dp[j][i - coin]);
+      }
+
+      dp[j][i] = Math.min(dp[j][i], dp[j - 1][i]);
+    }
+  }
+
+  return dp.at(-1).at(-1) === Infinity ? -1 : dp.at(-1).at(-1);
+};

From 0cdbba8b7bcaf5c35b57da4d7a8ab2df517c4508 Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Thu, 2 Jan 2025 07:58:14 +0900
Subject: [PATCH 06/10] refactor: feat: 21. Merge Two Sorted Lists

---
 merge-two-sorted-lists/gwbaik9717.js | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/merge-two-sorted-lists/gwbaik9717.js b/merge-two-sorted-lists/gwbaik9717.js
index 513778a83..e7d1ab988 100644
--- a/merge-two-sorted-lists/gwbaik9717.js
+++ b/merge-two-sorted-lists/gwbaik9717.js
@@ -30,16 +30,12 @@ var mergeTwoLists = function (list1, list2) {
     current = current.next;
   }
 
-  while (list1) {
-    current.next = new ListNode(list1.val);
-    list1 = list1.next;
-    current = current.next;
+  if (list1) {
+    current.next = list1;
   }
 
-  while (list2) {
-    current.next = new ListNode(list2.val);
-    list2 = list2.next;
-    current = current.next;
+  if (list2) {
+    current.next = list2;
   }
 
   return answer.next;

From 70f3ef181627a372d0079ec1b19983fd2edfee57 Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Thu, 2 Jan 2025 08:14:17 +0900
Subject: [PATCH 07/10] refactor: feat: 79. Word Search

---
 word-search/gwbaik9717.js | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/word-search/gwbaik9717.js b/word-search/gwbaik9717.js
index 182641028..2b1db0944 100644
--- a/word-search/gwbaik9717.js
+++ b/word-search/gwbaik9717.js
@@ -1,6 +1,6 @@
 // h: height of the board, w: width of the board, n: length of the word
 // Time complexity: O(h * w * 4**n)
-// Space complexity: O(h * w + n)
+// Space complexity: O(n)
 
 /**
  * @param {character[][]} board
@@ -15,10 +15,6 @@ var exist = function (board, word) {
   const dy = [1, 0, -1, 0];
   const dx = [0, 1, 0, -1];
 
-  const checked = Array.from({ length: h }, () =>
-    Array.from({ length: w }, () => 0)
-  );
-
   let answer = false;
 
   const dfs = (current, index) => {
@@ -28,7 +24,8 @@ var exist = function (board, word) {
     }
 
     const [cy, cx] = current;
-    checked[cy][cx] = 1;
+    const value = board[cy][cx];
+    board[cy][cx] = "";
 
     for (let i = 0; i < dy.length; i++) {
       const ny = cy + dy[i];
@@ -40,14 +37,14 @@ var exist = function (board, word) {
         ny < h &&
         nx >= 0 &&
         nx < w &&
-        checked[ny][nx] === 0 &&
+        board[ny][nx] &&
         word[ni] === board[ny][nx]
       ) {
         dfs([ny, nx], ni);
       }
     }
 
-    checked[cy][cx] = 0;
+    board[cy][cx] = value;
   };
 
   for (let i = 0; i < h; i++) {

From 6eb0ac0753ec9bca31221fac2b647f6ba2a664a7 Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Thu, 2 Jan 2025 08:45:14 +0900
Subject: [PATCH 08/10] refactor: feat: 322. Coin Change

---
 coin-change/gwbaik9717.js | 26 ++++++++------------------
 1 file changed, 8 insertions(+), 18 deletions(-)

diff --git a/coin-change/gwbaik9717.js b/coin-change/gwbaik9717.js
index e2b0b78a2..752060ad9 100644
--- a/coin-change/gwbaik9717.js
+++ b/coin-change/gwbaik9717.js
@@ -1,6 +1,6 @@
 // n: amount m: length of coins
 // Time complexity: O(n * m) + O(mlogm)
-// Space complexity: O(n * m)
+// Space complexity: O(n)
 
 /**
  * @param {number[]} coins
@@ -8,26 +8,16 @@
  * @return {number}
  */
 var coinChange = function (coins, amount) {
-  const dp = Array.from({ length: coins.length + 1 }, () =>
-    Array.from({ length: amount + 1 }, () => Infinity)
-  );
-  coins.sort((a, b) => a - b);
-
-  for (let i = 0; i < coins.length + 1; i++) {
-    dp[i][0] = 0;
-  }
+  const dp = Array.from({ length: amount + 1 }, () => Infinity);
+  dp[0] = 0;
 
-  for (let i = 1; i <= amount; i++) {
-    for (let j = 1; j <= coins.length; j++) {
-      const coin = coins[j - 1];
-
-      if (i >= coin) {
-        dp[j][i] = Math.min(dp[j][i], 1 + dp[j][i - coin]);
-      }
+  coins.sort((a, b) => a - b);
 
-      dp[j][i] = Math.min(dp[j][i], dp[j - 1][i]);
+  for (const coin of coins) {
+    for (let i = coin; i <= amount; i++) {
+      dp[i] = Math.min(dp[i], dp[i - coin] + 1);
     }
   }
 
-  return dp.at(-1).at(-1) === Infinity ? -1 : dp.at(-1).at(-1);
+  return dp.at(-1) === Infinity ? -1 : dp.at(-1);
 };

From 7812d91bbda845ce3541e5cca03e68d23012bad0 Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Fri, 3 Jan 2025 07:56:16 +0900
Subject: [PATCH 09/10] refactor: 21. Merge Two Sorted Lists

---
 merge-two-sorted-lists/gwbaik9717.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/merge-two-sorted-lists/gwbaik9717.js b/merge-two-sorted-lists/gwbaik9717.js
index e7d1ab988..b83246666 100644
--- a/merge-two-sorted-lists/gwbaik9717.js
+++ b/merge-two-sorted-lists/gwbaik9717.js
@@ -20,10 +20,10 @@ var mergeTwoLists = function (list1, list2) {
 
   while (list1 && list2) {
     if (list1.val < list2.val) {
-      current.next = new ListNode(list1.val);
+      current.next = list1;
       list1 = list1.next;
     } else {
-      current.next = new ListNode(list2.val);
+      current.next = list2;
       list2 = list2.next;
     }
 

From e7c0e56efc28f14d7271d0488a25bcd05038da43 Mon Sep 17 00:00:00 2001
From: Paik <gwbaik9717@icloud.com>
Date: Sat, 4 Jan 2025 09:28:45 +0900
Subject: [PATCH 10/10] refactor: 647. Palindromic Substrings

---
 palindromic-substrings/gwbaik9717.js | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/palindromic-substrings/gwbaik9717.js b/palindromic-substrings/gwbaik9717.js
index 6d65d5e8b..69e042bd4 100644
--- a/palindromic-substrings/gwbaik9717.js
+++ b/palindromic-substrings/gwbaik9717.js
@@ -10,34 +10,28 @@ var countSubstrings = function (s) {
   const dp = Array.from({ length: n }, () =>
     Array.from({ length: n }, () => false)
   );
+  let answer = 0;
 
   for (let end = 0; end < n; end++) {
     for (let start = end; start >= 0; start--) {
       if (start === end) {
         dp[start][end] = true;
+        answer++;
         continue;
       }
 
       if (start + 1 === end) {
         if (s[start] === s[end]) {
           dp[start][end] = true;
+          answer++;
         }
         continue;
       }
 
       if (s[start] === s[end] && dp[start + 1][end - 1]) {
         dp[start][end] = true;
-        continue;
-      }
-    }
-  }
-
-  let answer = 0;
-
-  for (let i = 0; i < n; i++) {
-    for (let j = 0; j < n; j++) {
-      if (dp[i][j]) {
         answer++;
+        continue;
       }
     }
   }