Leetcode Problem 1900-1999

1920. Build Array from Permutation 🌟

O(N) Time and O(N) Space solution

• For i=0 to n , simply do what they have asked to.
• Push_back(nums[nums[i]])

O(N) Time and O(1) Space optimization

• This is done to keep both old and new value together.
• going by the example of [5,0,1,2,3,4], n = 6(size of array)
• nums[i] = nums[i]+(n*(nums[nums[i]]%n));
• after this nums[0] will be 5 + 6*(4%6) = 5 + 24 = 29;
• now for next index calculation we might need the original value of num[0] which can be obtain by num[0]%6 = 29%6 = 5;
• if we want to get just the new value of num[0], we can get it by num[0]/6 = 29/6 = 4

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1929. Concatenation of Array 🌟

O(N) Time and O(N) Space solution

• We will use inbuilt function vector.insert() to concatenate the arrays.

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1971. Find if Path Exists in Graph 🌟

DFS

• Basic DFS with stack

UnionFind

• If path exist between 2 nodes then they are in same component.
• We can use UnionFind to know if source and destination are in same component.

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