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Formatted question description: https://leetcode.ca/all/2177.html

2177. Find Three Consecutive Integers That Sum to a Given Number (Medium)

Given an integer num, return three consecutive integers (as a sorted array) that sum to num. If num cannot be expressed as the sum of three consecutive integers, return an empty array.

 

Example 1:

Input: num = 33
Output: [10,11,12]
Explanation: 33 can be expressed as 10 + 11 + 12 = 33.
10, 11, 12 are 3 consecutive integers, so we return [10, 11, 12].

Example 2:

Input: num = 4
Output: []
Explanation: There is no way to express 4 as the sum of 3 consecutive integers.

 

Constraints:

  • 0 <= num <= 1015

Similar Questions:

Solution 1. Math

Let x be the first number of the 3 consecutive numbers. Then num = x + x + 1 + x + 2 = 3 * x + 3. Since x is an integer, num must be multiple of 3, and x = num / 3 - 1.

  • // OJ: https://leetcode.com/problems/find-three-consecutive-integers-that-sum-to-a-given-number/
// Time: O(1)
// Space: O(1)
class Solution {
public:
    vector<long long> sumOfThree(long long num) {
        if (num % 3) return {};
        long x = num / 3 - 1; 
        return {x, x + 1, x + 2};
    }
};

  • class Solution:
    def sumOfThree(self, num: int) -> List[int]:
        a, b = divmod(num, 3)
        return [] if b else [a - 1, a, a + 1]

############

# 2177. Find Three Consecutive Integers That Sum to a Given Number
# https://leetcode.com/problems/find-three-consecutive-integers-that-sum-to-a-given-number/

class Solution:
    def sumOfThree(self, num: int) -> List[int]:
        if num % 3 != 0: return []
        mid = num // 3
        return [mid - 1, mid, mid + 1]


  • class Solution {
    public long[] sumOfThree(long num) {
        if (num % 3 != 0) {
            return new long[] {};
        }
        long x = num / 3;
        return new long[] {x - 1, x, x + 1};
    }
}

  • func sumOfThree(num int64) []int64 {
	if num%3 != 0 {
		return []int64{}
	}
	x := num / 3
	return []int64{x - 1, x, x + 1}
}

  • function sumOfThree(num: number): number[] {
    if (num % 3) {
        return [];
    }
    const x = Math.floor(num / 3);
    return [x - 1, x, x + 1];
}

Or one-liner

  • // OJ: https://leetcode.com/problems/find-three-consecutive-integers-that-sum-to-a-given-number/
// Time: O(1)
// Space: O(1)
class Solution {
public:
    vector<long long> sumOfThree(long long num) {
        return num % 3 ? vector<long long>{} : vector<long long>{num / 3 - 1, num / 3, num / 3 + 1};
    }
};

  • class Solution:
    def sumOfThree(self, num: int) -> List[int]:
        a, b = divmod(num, 3)
        return [] if b else [a - 1, a, a + 1]

############

# 2177. Find Three Consecutive Integers That Sum to a Given Number
# https://leetcode.com/problems/find-three-consecutive-integers-that-sum-to-a-given-number/

class Solution:
    def sumOfThree(self, num: int) -> List[int]:
        if num % 3 != 0: return []
        mid = num // 3
        return [mid - 1, mid, mid + 1]


  • class Solution {
    public long[] sumOfThree(long num) {
        if (num % 3 != 0) {
            return new long[] {};
        }
        long x = num / 3;
        return new long[] {x - 1, x, x + 1};
    }
}

  • func sumOfThree(num int64) []int64 {
	if num%3 != 0 {
		return []int64{}
	}
	x := num / 3
	return []int64{x - 1, x, x + 1}
}

  • function sumOfThree(num: number): number[] {
    if (num % 3) {
        return [];
    }
    const x = Math.floor(num / 3);
    return [x - 1, x, x + 1];
}

Discuss

https://leetcode.com/problems/find-three-consecutive-integers-that-sum-to-a-given-number/discuss/1783380/C%2B%2B-Math-one-liner

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