1304. Find N Unique Integers Sum up to Zero

Problem Statement

Pattern:

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Solution

// simple approach
public int[] sumZero1(int n) {
	int[] res = new int[n];
	for (int i = 0 ; i < n-1 ; i++)
		res[i++] = i+1;
 
	// add last element -> -ve sum of elements b4 n
	res[--n] = -n * (n+1) / 2;
	return res;
}
 
// robust approach (n >= 10^5)
public int[] sumZero(int n) {
	int[] res = new int[n];
	for (int i = 0; i < n; i++)
		res[i] = 2*i - n +1;
	return res;
}

Notes

• First Appraoch is simple and straight fwd
  • Fill array with numbers upto n-1
  • last element is the negative sum of all the numbers
• Second approach is robust with large range of n
  • [Java/C++/Python] Find the Rule - LeetCode Discuss
  • Basically it will give you a patttern like this.
  • n = 3, [-2, 0, 2]
  • n = 4, [-3, -1, 1, 3]
  • n = 5, [-4, -2, 0, 2, 4]