[20180416] medium problems

Author: iamminji

README.md

@@ -36,6 +36,7 @@
 | [0103](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/description/)  | Binary Tree Zigzag Level Order Traversal  | medium     | python         |           |
 | [0107](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/description/)      | Binary Tree Level Order Traversal II      | easy       | python         |           |
 | [0111](https://leetcode.com/problems/minimum-depth-of-binary-tree/)      |  Minimum Depth of Binary Tree      | easy       | [python](🙂easy/0111.Minimum-Depth-of-Binary-Tree/minimum_depth_of_binary_tree.py)         |    tree       |
+| [0120](https://leetcode.com/problems/triangle/)         | Triangle        | medium       | [python](🤔medium/0120.Triangle/triangle.py)         |           |
 | [0121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)         | Best Time to Buy and Sell Stock        | easy       | [python](🙂easy/0121.Best-Time-to-Buy-and-Sell-Stock/best_time_to_buy_and_sell_stock.py)         |           |
 | [0122](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description)         | Best Time to Buy and Sell Stock II        | easy       | python         |           |
 | [0139](https://leetcode.com/problems/word-break/description/)                                | Word Break                                | medium     | python         |           |

🤔medium/0120.Triangle/triangle.py

@@ -0,0 +1,43 @@
+# 120. Triangle
+# https://leetcode.com/problems/triangle/
+
+from typing import List
+
+
+class Solution(object):
+    # triangle 에서 minimum path 를 구하는 문제다.
+    # 전형적인 dp 문제다.
+    def minimumTotal(self, triangle: List[List[int]]) -> int:
+        """
+        :type triangle: List[List[int]]
+        :rtype: int
+        """
+
+        height = len(triangle)
+
+        if height == 1:
+            return min(triangle[0])
+
+        # 현재 값의 최소 값은 바로 위의 (height-1) 값 과 바로 위의 옆에 값 의 최소 값 + 현재 값이다.
+        # 가장 끄트머리에 있는 것들만 예외 처리를 해주는 방식(끄트머리의 것들은 바로 위의 것만 영향을 받는다) 으로 top-down 으로 구했다.
+        for i in range(1, height):
+            for j in range(len(triangle[i])):
+                if j == 0:
+                    triangle[i][j] = triangle[i - 1][j] + triangle[i][j]
+                    continue
+                if j == len(triangle[i]) - 1:
+                    triangle[i][j] = triangle[i - 1][j - 1] + triangle[i][j]
+                    continue
+                triangle[i][j] = min(triangle[i - 1][j - 1], triangle[i - 1][j]) + triangle[i][j]
+
+        return min(triangle[height - 1])
+
+
+if __name__ == '__main__':
+    sol = Solution()
+    assert sol.minimumTotal([
+        [2],
+        [3, 4],
+        [6, 5, 7],
+        [4, 1, 8, 3]
+    ]) == 11