<p>A <strong>bit flip</strong> of a number <code>x</code> is choosing a bit in the binary representation of <code>x</code> and <strong>flipping</strong> it from either <code>0</code> to <code>1</code> or <code>1</code> to <code>0</code>.</p> <ul> <li>For example, for <code>x = 7</code>, the binary representation is <code>111</code> and we may choose any bit (including any leading zeros not shown) and flip it. We can flip the first bit from the right to get <code>110</code>, flip the second bit from the right to get <code>101</code>, flip the fifth bit from the right (a leading zero) to get <code>10111</code>, etc.</li> </ul> <p>Given two integers <code>start</code> and <code>goal</code>, return<em> the <strong>minimum</strong> number of <strong>bit flips</strong> to convert </em><code>start</code><em> to </em><code>goal</code>.</p> <p> </p> <p><strong>Example 1:</strong></p> <pre> <strong>Input:</strong> start = 10, goal = 7 <strong>Output:</strong> 3 <strong>Explanation:</strong> The binary representation of 10 and 7 are 1010 and 0111 respectively. We can convert 10 to 7 in 3 steps: - Flip the first bit from the right: 101<u>0</u> -> 101<u>1</u>. - Flip the third bit from the right: 1<u>0</u>11 -> 1<u>1</u>11. - Flip the fourth bit from the right: <u>1</u>111 -> <u>0</u>111. It can be shown we cannot convert 10 to 7 in less than 3 steps. Hence, we return 3.</pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> start = 3, goal = 4 <strong>Output:</strong> 3 <strong>Explanation:</strong> The binary representation of 3 and 4 are 011 and 100 respectively. We can convert 3 to 4 in 3 steps: - Flip the first bit from the right: 01<u>1</u> -> 01<u>0</u>. - Flip the second bit from the right: 0<u>1</u>0 -> 0<u>0</u>0. - Flip the third bit from the right: <u>0</u>00 -> <u>1</u>00. It can be shown we cannot convert 3 to 4 in less than 3 steps. Hence, we return 3. </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>0 <= start, goal <= 10<sup>9</sup></code></li> </ul>