add leetcode problem-cn part1

算法题（国内版）/problem (Chinese)/矩阵区域和 [matrix-block-sum].html

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+<p>给你一个 <code>m x n</code> 的矩阵 <code>mat</code> 和一个整数 <code>k</code> ，请你返回一个矩阵 <code>answer</code> ，其中每个 <code>answer[i][j]</code> 是所有满足下述条件的元素 <code>mat[r][c]</code> 的和： </p>
+
+<ul>
+	<li><code>i - k <= r <= i + k, </code></li>
+	<li><code>j - k <= c <= j + k</code> 且</li>
+	<li><code>(r, c)</code> 在矩阵内。</li>
+</ul>
+
+<p> </p>
+
+<p><strong>示例 1：</strong></p>
+
+<pre>
+<strong>输入：</strong>mat = [[1,2,3],[4,5,6],[7,8,9]], k = 1
+<strong>输出：</strong>[[12,21,16],[27,45,33],[24,39,28]]
+</pre>
+
+<p><strong>示例 2：</strong></p>
+
+<pre>
+<strong>输入：</strong>mat = [[1,2,3],[4,5,6],[7,8,9]], k = 2
+<strong>输出：</strong>[[45,45,45],[45,45,45],[45,45,45]]
+</pre>
+
+<p> </p>
+
+<p><strong>提示：</strong></p>
+
+<ul>
+	<li><code>m == mat.length</code></li>
+	<li><code>n == mat[i].length</code></li>
+	<li><code>1 <= m, n, k <= 100</code></li>
+	<li><code>1 <= mat[i][j] <= 100</code></li>
+</ul>