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            "title": "Number of Laser Beams in a Bank",
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            "content": "<p>Anti-theft security devices are activated inside a bank. You are given a <strong>0-indexed</strong> binary string array <code>bank</code> representing the floor plan of the bank, which is an <code>m x n</code> 2D matrix. <code>bank[i]</code> represents the <code>i<sup>th</sup></code> row, consisting of <code>&#39;0&#39;</code>s and <code>&#39;1&#39;</code>s. <code>&#39;0&#39;</code> means the cell is empty, while<code>&#39;1&#39;</code> means the cell has a security device.</p>\n\n<p>There is <strong>one</strong> laser beam between any <strong>two</strong> security devices <strong>if both</strong> conditions are met:</p>\n\n<ul>\n\t<li>The two devices are located on two <strong>different rows</strong>: <code>r<sub>1</sub></code> and <code>r<sub>2</sub></code>, where <code>r<sub>1</sub> &lt; r<sub>2</sub></code>.</li>\n\t<li>For <strong>each</strong> row <code>i</code> where <code>r<sub>1</sub> &lt; i &lt; r<sub>2</sub></code>, there are <strong>no security devices</strong> in the <code>i<sup>th</sup></code> row.</li>\n</ul>\n\n<p>Laser beams are independent, i.e., one beam does not interfere nor join with another.</p>\n\n<p>Return <em>the total number of laser beams in the bank</em>.</p>\n\n<p>&nbsp;</p>\n<p><strong>Example 1:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2021/12/24/laser1.jpg\" style=\"width: 400px; height: 368px;\" />\n<pre>\n<strong>Input:</strong> bank = [&quot;011001&quot;,&quot;000000&quot;,&quot;010100&quot;,&quot;001000&quot;]\n<strong>Output:</strong> 8\n<strong>Explanation:</strong> Between each of the following device pairs, there is one beam. In total, there are 8 beams:\n * bank[0][1] -- bank[2][1]\n * bank[0][1] -- bank[2][3]\n * bank[0][2] -- bank[2][1]\n * bank[0][2] -- bank[2][3]\n * bank[0][5] -- bank[2][1]\n * bank[0][5] -- bank[2][3]\n * bank[2][1] -- bank[3][2]\n * bank[2][3] -- bank[3][2]\nNote that there is no beam between any device on the 0<sup>th</sup> row with any on the 3<sup>rd</sup> row.\nThis is because the 2<sup>nd</sup> row contains security devices, which breaks the second condition.\n</pre>\n\n<p><strong>Example 2:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2021/12/24/laser2.jpg\" style=\"width: 244px; height: 325px;\" />\n<pre>\n<strong>Input:</strong> bank = [&quot;000&quot;,&quot;111&quot;,&quot;000&quot;]\n<strong>Output:</strong> 0\n<strong>Explanation:</strong> There does not exist two devices located on two different rows.\n</pre>\n\n<p>&nbsp;</p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>m == bank.length</code></li>\n\t<li><code>n == bank[i].length</code></li>\n\t<li><code>1 &lt;= m, n &lt;= 500</code></li>\n\t<li><code>bank[i][j]</code> is either <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>\n</ul>\n",
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            "hints": [
                "What is the commonality between security devices on the same row?",
                "Each device on the same row has the same number of beams pointing towards the devices on the next row with devices.",
                "If you were given an integer array where each element is the number of security devices on each row, can you solve it?",
                "Convert the input to such an array, skip any row with no security device, then find the sum of the product between adjacent elements."
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