From 3810e50ff0eb8b58d6e37dc970e012a61b83b24e Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Mon, 26 Aug 2024 22:45:04 -0400
Subject: [PATCH 1/9] Two Sum solution

---
 two-sum/kimyoung.js | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 two-sum/kimyoung.js

diff --git a/two-sum/kimyoung.js b/two-sum/kimyoung.js
new file mode 100644
index 000000000..11857e586
--- /dev/null
+++ b/two-sum/kimyoung.js
@@ -0,0 +1,14 @@
+var twoSum = function (nums, target) {
+    let map = new Map(); // create a map to store the number and index of each element
+    for(let i = 0; i < nums.length; i++) {
+        let diff = target - nums[i];
+        if(map.has(diff)) { // once the differnece is found, return both index
+            return [i, map.get(diff)];
+        } else { // otherwise add to map
+            map.set(nums[i], i)
+        }
+    }
+};
+
+// time - O(n) at worst, iterate through the entire nums array 
+// space - O(n) at worst, map the entire nums array

From 4e17a7390488a4632a675b70d9a5a3b9ac4fa71f Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Mon, 26 Aug 2024 22:52:37 -0400
Subject: [PATCH 2/9] Product of Array Except Self solution

---
 product-of-array-except-self/kimyoung.js | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 product-of-array-except-self/kimyoung.js

diff --git a/product-of-array-except-self/kimyoung.js b/product-of-array-except-self/kimyoung.js
new file mode 100644
index 000000000..7ddbf98f4
--- /dev/null
+++ b/product-of-array-except-self/kimyoung.js
@@ -0,0 +1,18 @@
+var productExceptSelf = function (nums) {
+    let result = new Array(nums.length).fill(0); // create a result array of length num
+    let pre = 1, post = 1; // default to 1 
+
+    for (let i = 0; i < nums.length; i++) { // fill the result array with prefix (multiplication of left values)
+        result[i] = pre;
+        pre *= nums[i];
+    }
+    for (let i = nums.length - 1; i >= 0; i--) { // multiply the postfix (multiplication of right values) to the result array in their corresponding index
+        result[i] *= post;
+        post *= nums[i];
+    }
+
+    return result;
+};
+
+// time - O(n) iterate through the nums array twice - 2n, remove constant which ends up to be n
+// space - O(1) result array not part of space complexity 
\ No newline at end of file

From 6dff87146e23b7b876ded65de9973c715758192a Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Mon, 26 Aug 2024 22:53:30 -0400
Subject: [PATCH 3/9] quick fix - add space on last line

---
 product-of-array-except-self/kimyoung.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/product-of-array-except-self/kimyoung.js b/product-of-array-except-self/kimyoung.js
index 7ddbf98f4..b6016c61c 100644
--- a/product-of-array-except-self/kimyoung.js
+++ b/product-of-array-except-self/kimyoung.js
@@ -15,4 +15,4 @@ var productExceptSelf = function (nums) {
 };
 
 // time - O(n) iterate through the nums array twice - 2n, remove constant which ends up to be n
-// space - O(1) result array not part of space complexity 
\ No newline at end of file
+// space - O(1) result array not part of space complexity

From 0363257a6f4b9a2c1d9a8fb5810b280879bcc1c2 Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Mon, 26 Aug 2024 23:21:39 -0400
Subject: [PATCH 4/9] Climbing Stairs solution

---
 climbing-stairs/kimyoung.js | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 climbing-stairs/kimyoung.js

diff --git a/climbing-stairs/kimyoung.js b/climbing-stairs/kimyoung.js
new file mode 100644
index 000000000..07e90dfcf
--- /dev/null
+++ b/climbing-stairs/kimyoung.js
@@ -0,0 +1,11 @@
+// found a pattern where the result is the addition of two previous elements,
+// but not sure if this is the expected answer
+var climbStairs = function (n) { 
+    let arr = new Array(n).fill(1);
+    for (let i = 2; i <= n; i++) {
+        arr[i] = arr[i - 2] + arr[i - 1];
+    }
+    return n === 1 ? 1 : arr[n];
+};
+
+// time - O(n) iterate up to n times
\ No newline at end of file

From f5536b5dba5e37ee8768d3b6adb81660dab7e75f Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Mon, 26 Aug 2024 23:23:28 -0400
Subject: [PATCH 5/9] quick fix - add end line break

---
 climbing-stairs/kimyoung.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/climbing-stairs/kimyoung.js b/climbing-stairs/kimyoung.js
index 07e90dfcf..325e7afd1 100644
--- a/climbing-stairs/kimyoung.js
+++ b/climbing-stairs/kimyoung.js
@@ -8,4 +8,5 @@ var climbStairs = function (n) {
     return n === 1 ? 1 : arr[n];
 };
 
-// time - O(n) iterate up to n times
\ No newline at end of file
+// time - O(n) iterate up to n times
+// space - O(n) creates an array upto n elements

From b4b98e94abd158d26e173d62df9da84e64db011e Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Tue, 27 Aug 2024 10:43:37 -0400
Subject: [PATCH 6/9] Combination Sum solution

---
 combination-sum/kimyoung.js | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 combination-sum/kimyoung.js

diff --git a/combination-sum/kimyoung.js b/combination-sum/kimyoung.js
new file mode 100644
index 000000000..292a12414
--- /dev/null
+++ b/combination-sum/kimyoung.js
@@ -0,0 +1,29 @@
+var combinationSum = function (candidates, target) {
+    let results = [];
+
+    function helper(idx, curr, total) {
+        // base case - when total = target push into results
+        if (total === target) {
+            results.push([...curr]);
+            return;
+        }
+        // base exit case - when the index is greater or equal to candidates or the total is greater than target, exit
+        if (idx >= candidates.length || total > target) {
+            return;
+        }
+
+        // recursive case
+        // case where we include the current value without advancing the index
+        curr.push(candidates[idx]);
+        helper(idx, curr, total + candidates[idx]);
+        curr.pop()
+        // case where we advance the index 
+        helper(idx + 1, curr, total);
+    }
+    helper(0, [], 0);
+    
+    return results;
+};
+
+// time - O(2^n) backtracking
+// space - O(1)
\ No newline at end of file

From 57b9908137c3d44451b571aa62739644c00833c4 Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Tue, 27 Aug 2024 10:44:02 -0400
Subject: [PATCH 7/9] quick fix - add end line break

---
 combination-sum/kimyoung.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/combination-sum/kimyoung.js b/combination-sum/kimyoung.js
index 292a12414..269444145 100644
--- a/combination-sum/kimyoung.js
+++ b/combination-sum/kimyoung.js
@@ -26,4 +26,4 @@ var combinationSum = function (candidates, target) {
 };
 
 // time - O(2^n) backtracking
-// space - O(1)
\ No newline at end of file
+// space - O(1)

From f5cfc084379bda433ba26d53feff1a5ce2ffb485 Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Wed, 28 Aug 2024 19:27:52 -0400
Subject: [PATCH 8/9] Coin Change solution

---
 coin-change/kimyoung.js | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 coin-change/kimyoung.js

diff --git a/coin-change/kimyoung.js b/coin-change/kimyoung.js
new file mode 100644
index 000000000..8084582bf
--- /dev/null
+++ b/coin-change/kimyoung.js
@@ -0,0 +1,24 @@
+var coinChange = function (coins, amount) {
+    // create a dp array that stores the minimum amount of coins used for each amount leading up to the target amount
+    // fill with array with amount + 1 as a default 
+    const dp = [0, ...new Array(amount).fill(amount + 1)];
+
+    // loop through the coins 
+    for (const coin of coins) {
+        // for each amount, assess how the current coin can modify the existing value within the dp array by comparing the min value
+        for (let i = 1; i <= amount; i++) {
+            // only works if coin is less than or equal to the assessing amount
+            if (coin <= i) {
+                // min comparison 
+                dp[i] = Math.min(dp[i], dp[i - coin] + 1);
+            }
+        }
+    }
+    // check target amount in dp array to see if it's the default value
+    // if it's default value, it means coin combination cannot lead up to target amount
+    // if it's not default value, that is the minimum required coin change to lead up to target amount
+    return dp[amount] === amount + 1 ? -1 : dp[amount];
+};
+
+// time - O(a * c) loops through amount * loops through coin
+// space - O(a) depends on the size of amount
\ No newline at end of file

From e5d46b2d83c01edc8ab256b902728fde5a4bef8e Mon Sep 17 00:00:00 2001
From: Young Kim <younghyun87@gmail.com>
Date: Wed, 28 Aug 2024 19:28:21 -0400
Subject: [PATCH 9/9] add end line break

---
 coin-change/kimyoung.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/coin-change/kimyoung.js b/coin-change/kimyoung.js
index 8084582bf..25bd04f53 100644
--- a/coin-change/kimyoung.js
+++ b/coin-change/kimyoung.js
@@ -21,4 +21,4 @@ var coinChange = function (coins, amount) {
 };
 
 // time - O(a * c) loops through amount * loops through coin
-// space - O(a) depends on the size of amount
\ No newline at end of file
+// space - O(a) depends on the size of amount