Odd Even Jump

Count how many starting indices can reach the end of an array by alternating odd/even jumps where an odd jump goes to the smallest-index j>i with arr[j] >= arr[i] and an even jump goes to the smallest-index j>i with arr[j] <= arr[i]. The core challenge is efficiently precomputing these next-higher/next-lower targets (e.g., via sorting + monotonic stack or an ordered map) and using DP to track which indices can reach the end.