Make Subarray

There is a canvas with $N$ total cells, and each cell can be painted white or black. Currently, the state of the board can be represented by a binary string $S$, where $S_i = 1$ if and only if the $i$-th call in the canvas is painted black, and $S_i = 0$ otherwise. You want the black cells to form a contiguous subarray, i.e. if cell $x$ and cell $y$ are coloured black, then all cells $z$ between