Move Zeroes

Maintain a stable prefix

Keep write = 0. Scan the array from left to right. Whenever nums[read] is nonzero, swap it with nums[write] when the indices differ, then increment write. At every point, positions before write contain exactly the nonzero values seen so far in their original order; positions from write through read are values displaced while the scan continues.

After the scan, all remaining positions are zero because each nonzero was moved ahead of them. This is O(n) time and O(1) extra space. A two-pass write-nonzeros-then-fill-zeros version is also stable and often simpler, but performs more writes. Test no zeros, all zeros, leading/trailing zeros, repeated values, and a length-one array. Clarify whether mutation is allowed; if not, a new array is required. Do not use an unstable partition because it can reorder [0, 1, 0, 3, 12] incorrectly.