# 1642-furthest-building-you-can-reach


Try it on <a href='https://leetcode.com/problems/1642-furthest-building-you-can-reach'>leetcode</a>

## Description
<div class="description">
<div><p>You are given an integer array <code>heights</code> representing the heights of buildings, some <code>bricks</code>, and some <code>ladders</code>.</p>

<p>You start your journey from building <code>0</code> and move to the next building by possibly using bricks or ladders.</p>

<p>While moving from building <code>i</code> to building <code>i+1</code> (<strong>0-indexed</strong>),</p>

<ul>
	<li>If the current building's height is <strong>greater than or equal</strong> to the next building's height, you do <strong>not</strong> need a ladder or bricks.</li>
	<li>If the current building's height is <b>less than</b> the next building's height, you can either use <strong>one ladder</strong> or <code>(h[i+1] - h[i])</code> <strong>bricks</strong>.</li>
</ul>

<p><em>Return the furthest building index (0-indexed) you can reach if you use the given ladders and bricks optimally.</em></p>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/10/27/q4.gif" style="width: 562px; height: 561px;">
<pre><strong>Input:</strong> heights = [4,2,7,6,9,14,12], bricks = 5, ladders = 1
<strong>Output:</strong> 4
<strong>Explanation:</strong> Starting at building 0, you can follow these steps:
- Go to building 1 without using ladders nor bricks since 4 &gt;= 2.
- Go to building 2 using 5 bricks. You must use either bricks or ladders because 2 &lt; 7.
- Go to building 3 without using ladders nor bricks since 7 &gt;= 6.
- Go to building 4 using your only ladder. You must use either bricks or ladders because 6 &lt; 9.
It is impossible to go beyond building 4 because you do not have any more bricks or ladders.
</pre>

<p><strong>Example 2:</strong></p>

<pre><strong>Input:</strong> heights = [4,12,2,7,3,18,20,3,19], bricks = 10, ladders = 2
<strong>Output:</strong> 7
</pre>

<p><strong>Example 3:</strong></p>

<pre><strong>Input:</strong> heights = [14,3,19,3], bricks = 17, ladders = 0
<strong>Output:</strong> 3
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= heights.length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= heights[i] &lt;= 10<sup>6</sup></code></li>
	<li><code>0 &lt;= bricks &lt;= 10<sup>9</sup></code></li>
	<li><code>0 &lt;= ladders &lt;= heights.length</code></li>
</ul>
</div>
</div>

## Solution(Python)
```Python
class Solution:
    def furthestBuilding(self, heights: List[int], bricks: int, ladders: int) -> int:
        heap = []
        for i in range(len(heights) - 1):
            diff = heights[i + 1] - heights[i]
            if diff > 0:
                if ladders > 0:
                    heappush(heap, diff)
                    ladders -= 1
                elif heap and diff > heap[0]:
                    heappush(heap, diff)
                    bricks -= heappop(heap)
                else:
                    bricks -= diff
                if bricks < 0:
                    return i
        return len(heights) - 1

```