2025-04-11 Daily Challenge

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In: DailyChallenge

Today I have done leetcode's April LeetCoding Challenge with cpp.

April LeetCoding Challenge 11

Description

Count Symmetric Integers

You are given two positive integers low and high.

An integer x consisting of 2 * n digits is symmetric if the sum of the first n digits of x is equal to the sum of the last n digits of x. Numbers with an odd number of digits are never symmetric.

Return the number of symmetric integers in the range [low, high].

 

Example 1:

Input: low = 1, high = 100
Output: 9
Explanation: There are 9 symmetric integers between 1 and 100: 11, 22, 33, 44, 55, 66, 77, 88, and 99.

Example 2:

Input: low = 1200, high = 1230
Output: 4
Explanation: There are 4 symmetric integers between 1200 and 1230: 1203, 1212, 1221, and 1230.

 

Constraints:

  • 1 <= low <= high <= 104

Solution

class Solution {
  static vector<int> result;
public:
  int countSymmetricIntegers(int low, int high) {
    return result[high] - result[low - 1];
  }
};

vector<int> Solution::result = []() {
  vector<int> result(10001);
  for(int i = 11; i < 10001; ++i) {
    result[i] = result[i - 1];
    if((i < 100 && i / 10 == i % 10) || (i > 1000 && (i / 1000 + i / 100 % 10 == i % 10 + i / 10 % 10))) result[i] += 1; 
  }
  return result;
}();

// Accepted
// 1967/1967 cases passed (4 ms)
// Your runtime beats 91.74 % of cpp submissions
// Your memory usage beats 84.15 % of cpp submissions (9.6 MB)
Algorithm