public class Solution
extends Object
1375 - Number of Times Binary String Is Prefix-Aligned\.
Medium
You have a **1-indexed** binary string of length `n` where all the bits are `0` initially. We will flip all the bits of this binary string (i.e., change them from `0` to `1`) one by one. You are given a **1-indexed** integer array `flips` where `flips[i]` indicates that the bit at index `i` will be flipped in the ith step.
A binary string is **prefix-aligned** if, after the ith step, all the bits in the **inclusive** range `[1, i]` are ones and all the other bits are zeros.
Return _the number of times the binary string is **prefix-aligned** during the flipping process_.
**Example 1:**
**Input:** flips = [3,2,4,1,5]
**Output:** 2
**Explanation:** The binary string is initially "00000".
After applying step 1: The string becomes "00100", which is not prefix-aligned.
After applying step 2: The string becomes "01100", which is not prefix-aligned.
After applying step 3: The string becomes "01110", which is not prefix-aligned.
After applying step 4: The string becomes "11110", which is prefix-aligned.
After applying step 5: The string becomes "11111", which is prefix-aligned.
We can see that the string was prefix-aligned 2 times, so we return 2.
**Example 2:**
**Input:** flips = [4,1,2,3]
**Output:** 1
**Explanation:** The binary string is initially "0000".
After applying step 1: The string becomes "0001", which is not prefix-aligned.
After applying step 2: The string becomes "1001", which is not prefix-aligned.
After applying step 3: The string becomes "1101", which is not prefix-aligned.
After applying step 4: The string becomes "1111", which is prefix-aligned.
We can see that the string was prefix-aligned 1 time, so we return 1.
**Constraints:**
* `n == flips.length`
* 1 <= n <= 5 * 104
* `flips` is a permutation of the integers in the range `[1, n]`.