feat: 1814_count_nice_pairs_in_an_array

1814_count_nice_pairs_in_an_array/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "count_nice_pairs_in_an_array"
+version = "0.1.0"

1814_count_nice_pairs_in_an_array/Cargo.toml

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+[package]
+name = "count_nice_pairs_in_an_array"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

1814_count_nice_pairs_in_an_array/src/lib.rs

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+pub struct Solution;
+
+impl Solution {
+    pub fn count_nice_pairs(nums: Vec<i32>) -> i32 {
+        const MOD: i64 = 1_000_000_007;
+
+        let mut groups = std::collections::HashMap::<i32, i64>::new();
+        for n in nums {
+            //    nums[i] + rev(nums[j]) == nums[j] + rev(nums[i])
+            // => nums[i] - rev(nums[i]) == nums[j] - rev(nums[j])
+            let num_sub_rev = n - Solution::rev(n);
+            groups
+                .entry(num_sub_rev)
+                .and_modify(|count| *count += 1)
+                .or_insert(1);
+        }
+
+        let result: i64 = groups.values().map(|count| count * (count - 1) / 2).sum();
+        (result % MOD) as i32
+    }
+
+    fn rev(mut num: i32) -> i32 {
+        let mut result = 0;
+        while num > 0 {
+            result *= 10;
+            result += num % 10;
+            num /= 10;
+        }
+        result
+    }
+}