LeetCode in Kotlin
1814. Count Nice Pairs in an Array
Medium
You are given an array nums that consists of non-negative integers. Let us define rev(x) as the reverse of the non-negative integer x. For example, rev(123) = 321, and rev(120) = 21. A pair of indices (i, j) is nice if it satisfies all of the following conditions:
0 <= i < j < nums.lengthnums[i] + rev(nums[j]) == nums[j] + rev(nums[i])
Return the number of nice pairs of indices. Since that number can be too large, return it modulo 109 + 7.
Example 1:
Input: nums = [42,11,1,97]
Output: 2
Explanation: The two pairs are:
-
(0,3) : 42 + rev(97) = 42 + 79 = 121, 97 + rev(42) = 97 + 24 = 121.
-
(1,2) : 11 + rev(1) = 11 + 1 = 12, 1 + rev(11) = 1 + 11 = 12.
Example 2:
Input: nums = [13,10,35,24,76]
Output: 4
Constraints:
1 <= nums.length <= 1050 <= nums[i] <= 109
Solution
@Suppress("NAME_SHADOWING")
class Solution {
private fun rev(n: Int): Int {
var n = n
var r = 0
while (n > 0) {
r = r * 10 + n % 10
n /= 10
}
return r
}
fun countNicePairs(nums: IntArray): Int {
val revMap = HashMap<Int, Int>()
var cnt = 0
for (num in nums) {
val lhs = num - rev(num)
val prevCnt = revMap.getOrDefault(lhs, 0)
cnt += prevCnt
val mod = 1000000007
cnt %= mod
revMap[lhs] = prevCnt + 1
}
return cnt
}
}