Simulation

LeetCode 3507 note: n is tiny, so simulate; the right side of a slice assignment must be a list

LeetCode 3494 note: for each potion, push forward to get the last wizard’s finish time (everyone must be free), then subtract backward to get each wizard’s finish time

LeetCode 735 note: scan left to right with a stack; only a right-moving top meeting a left-moving asteroid collides, the smaller explodes and equal sizes both do

LeetCode 3069 note: simulate the rule: the first two go to separate arrays, then each element joins the array whose last element is larger

LeetCode 1646 note: generate by the rules, nums[i // 2] at even i and nums[i // 2] + nums[i // 2 + 1] at odd i, handling n = 0 separately

LeetCode 59 note: keep four boundaries as in LC 54, but fill in 1 to n² instead of reading

LeetCode 54 note: keep four boundaries and walk right, down, left and up, shrinking a boundary after each side

LeetCode 43 note: num1[i] × num2[j] lands at position i + j + 1; accumulate into an array of length n + m and carry at the end

LeetCode 1103 note: simulate the rounds, giving i + 1 candies on the i-th turn, and hand all the rest to the current person when short

LeetCode 867 note: the transpose is n × m with res[j][i] = matrix[i][j]; in Python, zip(*matrix)

LeetCode 844 note: simulate backspaces with a stack; for O(1) space, walk from the end and count how many characters each # skips

LeetCode 682 note: keep valid scores on a stack; C removes the last, D adds its double, and + adds the sum of the last two