1583. Count Unhappy Friends: AC

Author: tan-wei

src/solution/mod.rs

@@ -1193,3 +1193,4 @@ mod s1577_number_of_ways_where_square_of_number_is_equal_to_product_of_two_numbe
 mod s1578_minimum_time_to_make_rope_colorful;
 mod s1579_remove_max_number_of_edges_to_keep_graph_fully_traversable;
 mod s1582_special_positions_in_a_binary_matrix;
+mod s1583_count_unhappy_friends;

src/solution/s1583_count_unhappy_friends.rs

@@ -0,0 +1,168 @@
+/**
+ * [1583] Count Unhappy Friends
+ *
+ * You are given a list of preferences for n friends, where n is always even.
+ * For each person i, preferences[i] contains a list of friends sorted in the order of preference. In other words, a friend earlier in the list is more preferred than a friend later in the list. Friends in each list are denoted by integers from 0 to n-1.
+ * All the friends are divided into pairs. The pairings are given in a list pairs, where pairs[i] = [xi, yi] denotes xi is paired with yi and yi is paired with xi.
+ * However, this pairing may cause some of the friends to be unhappy. A friend x is unhappy if x is paired with y and there exists a friend u who is paired with v but:
+ *
+ * 	x prefers u over y, and
+ * 	u prefers x over v.
+ *
+ * Return the number of unhappy friends.
+ *  
+ * Example 1:
+ *
+ * Input: n = 4, preferences = [[1, 2, 3], [3, 2, 0], [3, 1, 0], [1, 2, 0]], pairs = [[0, 1], [2, 3]]
+ * Output: 2
+ * Explanation:
+ * Friend 1 is unhappy because:
+ * - 1 is paired with 0 but prefers 3 over 0, and
+ * - 3 prefers 1 over 2.
+ * Friend 3 is unhappy because:
+ * - 3 is paired with 2 but prefers 1 over 2, and
+ * - 1 prefers 3 over 0.
+ * Friends 0 and 2 are happy.
+ *
+ * Example 2:
+ *
+ * Input: n = 2, preferences = [[1], [0]], pairs = [[1, 0]]
+ * Output: 0
+ * Explanation: Both friends 0 and 1 are happy.
+ *
+ * Example 3:
+ *
+ * Input: n = 4, preferences = [[1, 3, 2], [2, 3, 0], [1, 3, 0], [0, 2, 1]], pairs = [[1, 3], [0, 2]]
+ * Output: 4
+ *
+ *  
+ * Constraints:
+ *
+ * 	2 <= n <= 500
+ * 	n is even.
+ * 	preferences.length == n
+ * 	preferences[i].length == n - 1
+ * 	0 <= preferences[i][j] <= n - 1
+ * 	preferences[i] does not contain i.
+ * 	All values in preferences[i] are unique.
+ * 	pairs.length == n/2
+ * 	pairs[i].length == 2
+ * 	xi != yi
+ * 	0 <= xi, yi <= n - 1
+ * 	Each person is contained in exactly one pair.
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/count-unhappy-friends/
+// discuss: https://leetcode.com/problems/count-unhappy-friends/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    pub fn unhappy_friends(n: i32, preferences: Vec<Vec<i32>>, pairs: Vec<Vec<i32>>) -> i32 {
+        let n = n as usize;
+        let mut memo = vec![0; n];
+        for arr in &pairs {
+            let a = arr[0] as usize;
+            let b = arr[1] as usize;
+            memo[a] = b;
+            memo[b] = a;
+        }
+
+        let mut result = 0;
+        for arr in pairs {
+            let a = arr[0] as usize;
+            let b = arr[1] as usize;
+
+            let mut flag = false;
+            for &u in &preferences[a] {
+                let u = u as usize;
+                if u == b {
+                    break;
+                }
+
+                let v = memo[u];
+                for &candidate in &preferences[u] {
+                    let candidate = candidate as usize;
+                    if candidate == a {
+                        flag = true;
+                        break;
+                    } else if candidate == v {
+                        break;
+                    }
+                }
+
+                if flag {
+                    result += 1;
+                    break;
+                }
+            }
+
+            let mut flag = false;
+            for &u in &preferences[b] {
+                let u = u as usize;
+                if u == a {
+                    break;
+                }
+
+                let v = memo[u];
+                for &candidate in &preferences[u] {
+                    let candidate = candidate as usize;
+                    if candidate == b {
+                        flag = true;
+                        break;
+                    } else if candidate == v {
+                        break;
+                    }
+                }
+
+                if flag {
+                    result += 1;
+                    break;
+                }
+            }
+        }
+        result
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1583_example_1() {
+        let n = 4;
+        let preferences = vec![vec![1, 2, 3], vec![3, 2, 0], vec![3, 1, 0], vec![1, 2, 0]];
+        let pairs = vec![vec![0, 1], vec![2, 3]];
+
+        let result = 2;
+
+        assert_eq!(Solution::unhappy_friends(n, preferences, pairs), result);
+    }
+
+    #[test]
+    fn test_1583_example_2() {
+        let n = 2;
+        let preferences = vec![vec![1], vec![0]];
+        let pairs = vec![vec![1, 0]];
+
+        let result = 0;
+
+        assert_eq!(Solution::unhappy_friends(n, preferences, pairs), result);
+    }
+
+    #[test]
+    fn test_1583_example_3() {
+        let n = 4;
+        let preferences = vec![vec![1, 3, 2], vec![2, 3, 0], vec![1, 3, 0], vec![0, 2, 1]];
+        let pairs = vec![vec![1, 3], vec![0, 2]];
+
+        let result = 4;
+
+        assert_eq!(Solution::unhappy_friends(n, preferences, pairs), result);
+    }
+}