June20: nums of beautiful pairs [M]

Time: O(n * (k + logU)), n: len(nums), k: 10, U: max(nums)
Time of gcd: O(1)
Space: O(1)

daily/June20.cpp

@@ -0,0 +1,30 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+ public:
+  /**
+   * @brief LC: 2748: Number of Beautiful Pairs [M]
+   * Time: O(n*(k + logU)), n: len(nums), k = 10, U=max(nums)
+   * Time complexity of gcd is O(1)
+   * Space: O(k)
+   *
+   * @param nums
+   * @return int
+   */
+  int countBeautifulPairs(vector<int>& nums) {
+    int ans = 0, cnt[10]{};
+    for (int x : nums) {
+      for (int y = 1; y < 10; y++) {
+        if (cnt[y] && gcd(y, x % 10) == 1) {
+          ans += cnt[y];
+        }
+      }
+      while (x >= 10) {
+        x /= 10;
+      }
+      cnt[x]++;  // count times of highest
+    }
+    return ans;
+  }
+};