Question

2180. Count Integers With Even Digit Sum

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Description

Given a positive integer num, return _the number of positive integers less than or equal to_ num _whose digit sums are even_.

The digit sum of a positive integer is the sum of all its digits.

 

Example 1:

Input: num = 4
Output: 2
Explanation:
The only integers less than or equal to 4 whose digit sums are even are 2 and 4.  

Example 2:

Input: num = 30
Output: 14
Explanation:
The 14 integers less than or equal to 30 whose digit sums are even are
2, 4, 6, 8, 11, 13, 15, 17, 19, 20, 22, 24, 26, and 28.

 

Constraints:

• 1 <= num <= 1000

Solutions

Solution 1

class Solution:
  def countEven(self, num: int) -> int:
    ans = 0
    for x in range(1, num + 1):
      s = 0
      while x:
        s += x % 10
        x //= 10
      ans += s % 2 == 0
    return ans

class Solution {
  public int countEven(int num) {
    int ans = 0;
    for (int i = 1; i <= num; ++i) {
      int s = 0;
      for (int x = i; x > 0; x /= 10) {
        s += x % 10;
      }
      if (s % 2 == 0) {
        ++ans;
      }
    }
    return ans;
  }
}

class Solution {
public:
  int countEven(int num) {
    int ans = 0;
    for (int i = 1; i <= num; ++i) {
      int s = 0;
      for (int x = i; x; x /= 10) {
        s += x % 10;
      }
      ans += s % 2 == 0;
    }
    return ans;
  }
};

func countEven(num int) (ans int) {
  for i := 1; i <= num; i++ {
    s := 0
    for x := i; x > 0; x /= 10 {
      s += x % 10
    }
    if s%2 == 0 {
      ans++
    }
  }
  return
}

function countEven(num: number): number {
  let ans = 0;
  for (let i = 1; i <= num; ++i) {
    let s = 0;
    for (let x = i; x; x = Math.floor(x / 10)) {
      s += x % 10;
    }
    if (s % 2 == 0) {
      ++ans;
    }
  }
  return ans;
}

Solution 2

class Solution:
  def countEven(self, num: int) -> int:
    ans = num // 10 * 5 - 1
    x, s = num // 10, 0
    while x:
      s += x % 10
      x //= 10
    ans += (num % 10 + 2 - (s & 1)) >> 1
    return ans

class Solution {
  public int countEven(int num) {
    int ans = num / 10 * 5 - 1;
    int s = 0;
    for (int x = num / 10; x > 0; x /= 10) {
      s += x % 10;
    }
    ans += (num % 10 + 2 - (s & 1)) >> 1;
    return ans;
  }
}

class Solution {
public:
  int countEven(int num) {
    int ans = num / 10 * 5 - 1;
    int s = 0;
    for (int x = num / 10; x > 0; x /= 10) {
      s += x % 10;
    }
    ans += (num % 10 + 2 - (s & 1)) >> 1;
    return ans;
  }
};

func countEven(num int) (ans int) {
  ans = num/10*5 - 1
  s := 0
  for x := num / 10; x > 0; x /= 10 {
    s += x % 10
  }
  ans += (num%10 + 2 - (s & 1)) >> 1
  return
}

function countEven(num: number): number {
  let ans = Math.floor(num / 10) * 5 - 1;
  let s = 0;
  for (let x = Math.floor(num / 10); x; x = Math.floor(x / 10)) {
    s += x % 10;
  }
  ans += ((num % 10) + 2 - (s & 1)) >> 1;
  return ans;
}