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# 1375. Bulb Switcher III

<https://leetcode.com/problems/bulb-switcher-iii>

## Description

There is a room with `n` bulbs, numbered from `1` to `n`, arranged in a row from left to right. Initially, all the bulbs are turned off.

At moment `k` (for `k` from `0` to `n - 1`), we turn on the `light[k]` bulb. A bulb **changes color to blue** only if it is on and all the previous bulbs (to the left) are turned on too.

Return the number of moments in which **all turned-on** bulbs **are blue.**

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/02/29/sample_2_1725.png)

```
**Input:** light = [2,1,3,5,4]
**Output:** 3
**Explanation:** All bulbs turned on, are blue at the moment 1, 2 and 4.
```

**Example 2:**

```
**Input:** light = [3,2,4,1,5]
**Output:** 2
**Explanation:** All bulbs turned on, are blue at the moment 3, and 4 (index-0).
```

**Example 3:**

```
**Input:** light = [4,1,2,3]
**Output:** 1
**Explanation:** All bulbs turned on, are blue at the moment 3 (index-0).
Bulb 4th changes to blue at the moment 3.
```

**Example 4:**

```
**Input:** light = [2,1,4,3,6,5]
**Output:** 3
```

**Example 5:**

```
**Input:** light = [1,2,3,4,5,6]
**Output:** 6
```

**Constraints:**

* `n == light.length`
* `1 <= n <= 5 * 104`
* `light` is a permutation of the numbers in the range `[1, n]`

## ac

```java
```