1920. Build Array from Permutation

Problem Statement

Build Array from Permutation - LeetCode

Pattern: Pattern 2 values in 1 variable

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Solution

public int[] buildArray(int[] nums) {
	int n = nums.length;
	for (int i = 0; i < n; i++) {
		// nums[nums[i]] is the supposed correct location of nums[i]
		// nums[nums[i]] % n reverses this 👇 black magic we did to it, in case we did, otherwise same value.
		nums[i] = nums[i] + n * (nums[nums[i]] % n);
		
		// to store a and b in a
		// a' = a + (b * k)   - where k is some constant larger than both a and b, in this case we use nums.length
		// how are both a and b stored in a?
		// well a' % k  will give you a
		// a' / k will give you b !!
		
	}
	
	for (int i = 0; i < n; i++) {
		nums[i] = nums[i] / n;
	}
	return nums;
}

Notes

• The whole idea is to store 2 number inside of a single number
• reversing black magic : restores the earlier number if it has already been altered