Next greater element: the stack of pending indices, step by step
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input [2, 1, 2, 4, 3]
  i=0 value=2: push 0   pending(top first) = [0]
  i=1 value=1: push 1   pending(top first) = [1, 0]
  i=2 value=2: pop index 1 (value 1) -> its answer is 2; push 2   pending(top first) = [2, 0]
  i=3 value=4: pop index 2 (value 2) -> its answer is 4; pop index 0 (value 2) -> its answer is 4; push 3   pending(top first) = [3]
  i=4 value=3: push 4   pending(top first) = [4, 3]
  indices still pending have no greater element to their right: [4, 3] -> stay -1
result [4, 2, 4, -1, -1]

dailyTemperatures [73, 74, 75, 71, 69, 72, 76, 73]
  = [1, 1, 4, 2, 1, 1, 0, 0]

nextGreaterCircular [1, 2, 1] = [2, -1, 2]
nextGreaterSubset [4, 1, 2] within [1, 3, 4, 2] = [-1, 3, -1]