20241117 finished.

src/problem/mod.rs

@@ -320,3 +320,5 @@ mod p3249_count_the_number_of_good_nodes;
 mod p3239_minimum_number_of_flips_to_make_binary_grid_palindromic_i;
 
 mod p3240_minimum_number_of_flips_to_make_binary_grid_palindromic_ii;
+
+mod p825_friends_of_appropriate_ages;

src/problem/p825_friends_of_appropriate_ages.rs

@@ -0,0 +1,62 @@
+/**
+ * [825] Friends Of Appropriate Ages
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn num_friend_requests(ages: Vec<i32>) -> i32 {
+        let n = ages.len();
+        let mut ages = ages;
+        ages.sort_unstable();
+
+        let mut result = 0;
+
+        for i in (0..n).rev() {
+            let lower_bound = ages[i] / 2 + 7;
+            if lower_bound >= ages[i] {
+                continue;
+            }
+
+            let mut j = i + 1;
+            while j < n && ages[j] == ages[i] {
+                result += 1;
+                j += 1;
+            }
+
+            match ages.binary_search(&lower_bound) {
+                Ok(pos) => {
+                    let mut pos = pos;
+                    while pos + 1 < n && ages[pos] == ages[pos + 1] {
+                        pos += 1;
+                    }
+
+                    result += i - pos - 1;
+                }
+                Err(pos) => {
+                    result += i - pos;
+                }
+            }
+        }
+
+        result as i32
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_825() {
+        assert_eq!(2, Solution::num_friend_requests(vec![16, 16]));
+        assert_eq!(2, Solution::num_friend_requests(vec![16, 17, 18]));
+        assert_eq!(
+            3,
+            Solution::num_friend_requests(vec![20, 30, 100, 110, 120])
+        );
+    }
+}