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leetcode/3329-find-the-length-of-the-longest-common-prefix/README.md

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+<p>You are given two arrays with <strong>positive</strong> integers <code>arr1</code> and <code>arr2</code>.</p>
+
+<p>A <strong>prefix</strong> of a positive integer is an integer formed by one or more of its digits, starting from its <strong>leftmost</strong> digit. For example, <code>123</code> is a prefix of the integer <code>12345</code>, while <code>234</code> is <strong>not</strong>.</p>
+
+<p>A <strong>common prefix</strong> of two integers <code>a</code> and <code>b</code> is an integer <code>c</code>, such that <code>c</code> is a prefix of both <code>a</code> and <code>b</code>. For example, <code>5655359</code> and <code>56554</code> have a common prefix <code>565</code> while <code>1223</code> and <code>43456</code> <strong>do not</strong> have a common prefix.</p>
+
+<p>You need to find the length of the <strong>longest common prefix</strong> between all pairs of integers <code>(x, y)</code> such that <code>x</code> belongs to <code>arr1</code> and <code>y</code> belongs to <code>arr2</code>.</p>
+
+<p>Return <em>the length of the <strong>longest</strong> common prefix among all pairs</em>.<em> If no common prefix exists among them</em>, <em>return</em> <code>0</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr1 = [1,10,100], arr2 = [1000]
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> There are 3 pairs (arr1[i], arr2[j]):
+- The longest common prefix of (1, 1000) is 1.
+- The longest common prefix of (10, 1000) is 10.
+- The longest common prefix of (100, 1000) is 100.
+The longest common prefix is 100 with a length of 3.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr1 = [1,2,3], arr2 = [4,4,4]
+<strong>Output:</strong> 0
+<strong>Explanation:</strong> There exists no common prefix for any pair (arr1[i], arr2[j]), hence we return 0.
+Note that common prefixes between elements of the same array do not count.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= arr1.length, arr2.length &lt;= 5 * 10<sup>4</sup></code></li>
+	<li><code>1 &lt;= arr1[i], arr2[i] &lt;= 10<sup>8</sup></code></li>
+</ul>

leetcode/3329-find-the-length-of-the-longest-common-prefix/solution.rs

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+impl Solution {
+    pub fn longest_common_prefix(arr1: Vec<i32>, arr2: Vec<i32>) -> i32 {
+        use std::collections::HashSet;
+        let mut s1 = HashSet::new();
+        let mut s2 = HashSet::new();
+        for mut x in arr1 {
+            while x > 0 {
+                s1.insert(x);
+                x /= 10;
+            }
+        }
+        for mut x in arr2 {
+            while x > 0 {
+                s2.insert(x);
+                x /= 10;
+            }
+        }
+        let mut ret = 0;
+        if let Some(&x) = s1.intersection(&s2).max() {
+            let mut x = x;
+            while x > 0 {
+                ret += 1;
+                x /= 10;
+            }
+        }
+        return ret;
+    }
+}