Leetcode Problem 1800-1899

1832. Check if the Sentence Is Pangram 🌟

O(N) Time O(N) Space Solution

• Create a set and check if its length is exactly 26 or not.

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1854. Maximum Population Year 🌟

O(N) Time and O(N) Space

• We can mark the start and end of each life as +1 and -1 on the timeline.
• Then, we go through timeline from 1950 to 2050 and accumulate the current population for each year.

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1886. Determine Whether Matrix Can Be Obtained By Rotation 🌟

O(N^2) Time solution

• Suppose we are at index i, j, let us find a relation of this position with it’s position in various rotations. i. e

- 0 deg rotation : i, j will point to i, j
- 90 deg rotation : i, j will point to j, n - i - 1
- 180 deg rotation : i, j will point to n - i - 1, n - j - 1
- 270 deg rotation : i, j will point to n - j - 1, i

• We denote these rotations by boolean variables, initially we assume all these rotations are valid, so we set them all to true. Here

c[0] -> 0 deg rotation,
c[1] -> 90 deg,
c[2] -> 180 deg,
c[3] -> 270 deg

• Then, we loop over all elements and check if that particular rotation is valid or not. If not, we turn it to false.
• In the end, we simply check if any of the rotations is still possible or not.

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