feat: add solution 498. Diagonal Traverse

Author: tzuyi0817

solutions/498. Diagonal Traverse/README.md

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+# [498. Diagonal Traverse](https://leetcode.com/problems/diagonal-traverse)
+
+## Description
+
+<div class="elfjS" data-track-load="description_content"><p>Given an <code>m x n</code> matrix <code>mat</code>, return <em>an array of all the elements of the array in a diagonal order</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2021/04/10/diag1-grid.jpg" style="width: 334px; height: 334px;">
+<pre><strong>Input:</strong> mat = [[1,2,3],[4,5,6],[7,8,9]]
+<strong>Output:</strong> [1,2,4,7,5,3,6,8,9]
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre><strong>Input:</strong> mat = [[1,2],[3,4]]
+<strong>Output:</strong> [1,2,3,4]
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>m == mat.length</code></li>
+	<li><code>n == mat[i].length</code></li>
+	<li><code>1 &lt;= m, n &lt;= 10<sup>4</sup></code></li>
+	<li><code>1 &lt;= m * n &lt;= 10<sup>4</sup></code></li>
+	<li><code>-10<sup>5</sup> &lt;= mat[i][j] &lt;= 10<sup>5</sup></code></li>
+</ul>
+</div>
+
+<p>&nbsp;</p>
+
+## Solutions
+
+**Solution: `Simulation`**
+
+- Time complexity: <em>O(mn)</em>
+- Space complexity: <em>O(mn)</em>
+
+<p>&nbsp;</p>
+
+### **JavaScript**
+
+```js
+/**
+ * @param {number[][]} mat
+ * @return {number[]}
+ */
+const findDiagonalOrder = function (mat) {
+  const m = mat.length;
+  const n = mat[0].length;
+  const result = [];
+  let row = 0;
+  let col = 0;
+  let direction = 1;
+
+  for (let index = 0; index < m * n; index++) {
+    let nextRow = row - direction;
+    let nextCol = col + direction;
+
+    if (nextCol < 0) {
+      nextCol = nextRow > m - 1 ? 1 : 0;
+      nextRow = Math.min(m - 1, nextRow);
+      direction *= -1;
+    } else if (nextCol >= n) {
+      nextCol = n - 1;
+      nextRow = row + 1;
+      direction *= -1;
+    } else if (nextRow < 0) {
+      nextRow = 0;
+      direction *= -1;
+    } else if (nextRow >= m) {
+      nextRow = m - 1;
+      nextCol = col + 1;
+      direction *= -1;
+    }
+
+    result[index] = mat[row][col];
+    row = nextRow;
+    col = nextCol;
+  }
+
+  return result;
+};
+```

solutions/498. Diagonal Traverse/solution.js

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+/**
+ * @param {number[][]} mat
+ * @return {number[]}
+ */
+const findDiagonalOrder = function (mat) {
+  const m = mat.length;
+  const n = mat[0].length;
+  const result = [];
+  let row = 0;
+  let col = 0;
+  let direction = 1;
+
+  for (let index = 0; index < m * n; index++) {
+    let nextRow = row - direction;
+    let nextCol = col + direction;
+
+    if (nextCol < 0) {
+      nextCol = nextRow > m - 1 ? 1 : 0;
+      nextRow = Math.min(m - 1, nextRow);
+      direction *= -1;
+    } else if (nextCol >= n) {
+      nextCol = n - 1;
+      nextRow = row + 1;
+      direction *= -1;
+    } else if (nextRow < 0) {
+      nextRow = 0;
+      direction *= -1;
+    } else if (nextRow >= m) {
+      nextRow = m - 1;
+      nextCol = col + 1;
+      direction *= -1;
+    }
+
+    result[index] = mat[row][col];
+    row = nextRow;
+    col = nextCol;
+  }
+
+  return result;
+};