Update: description

Author: openset

problems/last-stone-weight-ii/README.md

@@ -44,3 +44,16 @@ we can combine 1 and 1 to get 0 so the array converts to [1] then that's the
 	<li><code>1 &lt;= stones.length &lt;= 30</code></li>
 	<li><code>1 &lt;= stones[i] &lt;= 100</code></li>
 </ol>
+
+### Related Topics
+  [[Dynamic Programming](https://github.com/openset/leetcode/tree/master/tag/dynamic-programming/README.md)]
+
+### Hints
+<details>
+<summary>Hint 1</summary>
+Think of the final answer as a sum of weights with + or - sign symbols infront of each weight.  Actually, all sums with 1 of each sign symbol are possible.
+</details>
+<details>
+<summary>Hint 2</summary>
+Use dynamic programming: for every possible sum with N stones, those sums +x or -x is possible with N+1 stones, where x is the value of the newest stone.  (This overcounts sums that are all positive or all negative, but those don't matter.)
+</details>

problems/range-sum-query-2d-immutable/README.md

@@ -14,7 +14,7 @@
 <p>Given a 2D matrix <i>matrix</i>, find the sum of the elements inside the rectangle defined by its upper left corner (<i>row</i>1, <i>col</i>1) and lower right corner (<i>row</i>2, <i>col</i>2).</p>
 
 <p>
-<img src="/static/images/courses/range_sum_query_2d.png" border="0" alt="Range Sum Query 2D" /><br />
+<img src="https://assets.leetcode-cn.com/aliyun-lc-upload/original_images/range_sum_query_2d.png" border="0" alt="Range Sum Query 2D" /><br />
 <small>The above rectangle (with the red border) is defined by (row1, col1) = <b>(2, 1)</b> and (row2, col2) = <b>(4, 3)</b>, which contains sum = <b>8</b>.</small>
 </p>