Outside-In String Reordering

Reorder a string by taking characters alternately from its left and right ends: first character, last character, second character, second-to-last character, and so on until every character is used. Requirements Input: a string. Produce a new string by taking the first character, then the last character, then the second character, then the second-to-last character, continuing inward in that order. Use every input character exactly once. For an odd-length string, append the unpaired center character last. Examples input: abcde output: aebdc Notes Two-pointer sweep: left starts at 0, right at len(s) - 1; alternately append s[left] (then advance) and s[right] (then retreat) while left < right, and append the single center character once left == right. The only real bug surface is the odd-length center: emitting it inside the alternating loop double-appends it. Exit the loop on left == right and append once. Preparation Reproduce the given example by hand and mark the source index used for each output position. Implement the inward traversal and verify that the center character is emitted exactly once.