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1572:矩阵对角线元素的和

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src/main/java/leetcode/editor/cn/MatrixDiagonalSum.java Normal file
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//<p>给你一个正方形矩阵 <code>mat</code>，请你返回矩阵对角线元素的和。</p>
//
//<p>请你返回在矩阵主对角线上的元素和副对角线上且不在主对角线上元素的和。</p>
//
//<p>&nbsp;</p>
//
//<p><strong>示例&nbsp; 1：</strong></p>
//
//<p><img alt="" src="https://assets.leetcode.com/uploads/2020/08/14/sample_1911.png" style="height:174px; width:336px" /></p>
//
//<pre>
//<strong>输入：</strong>mat = [[<strong>1</strong>,2,<strong>3</strong>],
//&nbsp; [4,<strong>5</strong>,6],
//&nbsp; [<strong>7</strong>,8,<strong>9</strong>]]
//<strong>输出：</strong>25
//<strong>解释：</strong>对角线的和为：1 + 5 + 9 + 3 + 7 = 25
//请注意，元素 mat[1][1] = 5 只会被计算一次。
//</pre>
//
//<p><strong>示例&nbsp; 2：</strong></p>
//
//<pre>
//<strong>输入：</strong>mat = [[<strong>1</strong>,1,1,<strong>1</strong>],
//&nbsp; [1,<strong>1</strong>,<strong>1</strong>,1],
//&nbsp; [1,<strong>1</strong>,<strong>1</strong>,1],
//&nbsp; [<strong>1</strong>,1,1,<strong>1</strong>]]
//<strong>输出：</strong>8
//</pre>
//
//<p><strong>示例 3：</strong></p>
//
//<pre>
//<strong>输入：</strong>mat = [[<strong>5</strong>]]
//<strong>输出：</strong>5
//</pre>
//
//<p>&nbsp;</p>
//
//<p><strong>提示：</strong></p>
//
//<ul>
// <li><code>n == mat.length == mat[i].length</code></li>
// <li><code>1 &lt;= n &lt;= 100</code></li>
// <li><code>1 &lt;= mat[i][j] &lt;= 100</code></li>
//</ul>
//<div><div>Related Topics</div><div><li>数组</li><li>矩阵</li></div></div><br><div><li>👍 50</li><li>👎 0</li></div>
package leetcode.editor.cn;
// 1572:矩阵对角线元素的和
public class MatrixDiagonalSum {
public static void main(String[] args) {
Solution solution = new MatrixDiagonalSum().new Solution();
// TO TEST
}
//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
public int diagonalSum(int[][] mat) {
int sum = 0;
int size = mat.length;
for (int i = 0; i < size; i++) {
sum += mat[i][i] + mat[size - 1 - i][i];
}
return size % 2 == 0 ? sum : sum - mat[size / 2][size / 2];
}
}
//leetcode submit region end(Prohibit modification and deletion)
}

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src/main/java/leetcode/editor/cn/doc/content/MatrixDiagonalSum.md Normal file
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<p>给你一个正方形矩阵 <code>mat</code>，请你返回矩阵对角线元素的和。</p>
<p>请你返回在矩阵主对角线上的元素和副对角线上且不在主对角线上元素的和。</p>
<p>&nbsp;</p>
<p><strong>示例&nbsp; 1：</strong></p>
<p><img alt="" src="https://assets.leetcode.com/uploads/2020/08/14/sample_1911.png" style="height:174px; width:336px" /></p>
<pre>
<strong>输入：</strong>mat = [[<strong>1</strong>,2,<strong>3</strong>],
&nbsp; [4,<strong>5</strong>,6],
&nbsp; [<strong>7</strong>,8,<strong>9</strong>]]
<strong>输出：</strong>25
<strong>解释：</strong>对角线的和为：1 + 5 + 9 + 3 + 7 = 25
请注意，元素 mat[1][1] = 5 只会被计算一次。
</pre>
<p><strong>示例&nbsp; 2：</strong></p>
<pre>
<strong>输入：</strong>mat = [[<strong>1</strong>,1,1,<strong>1</strong>],
&nbsp; [1,<strong>1</strong>,<strong>1</strong>,1],
&nbsp; [1,<strong>1</strong>,<strong>1</strong>,1],
&nbsp; [<strong>1</strong>,1,1,<strong>1</strong>]]
<strong>输出：</strong>8
</pre>
<p><strong>示例 3：</strong></p>
<pre>
<strong>输入：</strong>mat = [[<strong>5</strong>]]
<strong>输出：</strong>5
</pre>
<p>&nbsp;</p>
<p><strong>提示：</strong></p>
<ul>
<li><code>n == mat.length == mat[i].length</code></li>
<li><code>1 &lt;= n &lt;= 100</code></li>
<li><code>1 &lt;= mat[i][j] &lt;= 100</code></li>
</ul>
<div><div>Related Topics</div><div><li>数组</li><li>矩阵</li></div></div><br><div><li>👍 50</li><li>👎 0</li></div>