Implement Q43, 322

dynamic_programming/322_coin_change.md

@@ -2,11 +2,28 @@
 
 ## Question
 
-[\[Medium\] 322. Coin Change](https://leetcode.com/problems/coin-change/)
+[[Medium] 322. Coin Change](https://leetcode.com/problems/coin-change/)
 
 ## Thought
 
 ## Code
 
 ```python
+class Solution:
+    def coinChange(self, coins: List[int], amount: int) -> int:
+        dp = [-1]*(amount+1)
+
+        dp[0] = 0
+        for num in range(1, amount+1):
+            min_val = 2**31-1
+
+            for coin in coins:
+                if num - coin >= 0 and dp[num-coin] != -1:
+                    min_val = min(min_val, dp[num-coin]+1)
+
+            if min_val == 2**31-1:
+                min_val = -1
+            dp[num] = min_val
+
+        return dp[amount]
 ```

dynamic_programming/42_trapping_rain_water.md

@@ -2,11 +2,34 @@
 
 ## Question
 
-[\[Hard\] 42. Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/)
+[[Hard] 42. Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/)
 
 ## Thought
 
 ## Code
 
 ```python
+class Solution:
+    def trap(self, height: List[int]) -> int:
+        area = 0
+        left_max, right_max = 0, 0
+        left, right = 0, len(height)-1
+
+        while left < right:
+            if height[left] < height[right]:
+                if height[left] >= left_max:
+                    left_max = height[left]
+                else:
+                    area += left_max - height[left]
+
+                left += 1
+            else:
+                if height[right] >= right_max:
+                    right_max = height[right]
+                else:
+                    area += right_max - height[right]
+
+                right -= 1
+
+        return area
 ```