algorithm-neet-code-top-150-python-visual/visual/0704_binary_search.html at main · kimtth/algorithm-neet-code-top-150-python-visual · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>LC 704: Binary Search - Algorithm Visualization</title>
    <link rel="stylesheet" href="styles.css">
    <script src="https://d3js.org/d3.v7.min.js"></script>
</head>
<body>
    <div class="container">
        <div class="problem-info">
            <h1><span class="problem-number">#704</span> Binary Search</h1>
            <p>Given a sorted array of integers and a target, return the index of the target if found, otherwise return -1. Must run in O(log n) time.</p>
            <div class="problem-meta">
                <span class="meta-tag">📁 Array</span>
                <span class="meta-tag">🔍 Binary Search</span>
                <span class="meta-tag">⏱️ O(log n)</span>
            </div>
            <div class="file-ref">
                📄 Python: <code>python/0704_binary_search/0704_binary_search.py</code>
            </div>
            </div>

        <div class="explanation-panel">
            <h4>🧠 How It Works (Layman's Terms)</h4>
            <p>Imagine looking for a word in a dictionary - you don't start from page 1:</p>
            <ul>
                <li><strong>Open to middle:</strong> Check if target is before or after the middle</li>
                <li><strong>Too small:</strong> Target is in the right half → ignore left half</li>
                <li><strong>Too big:</strong> Target is in the left half → ignore right half</li>
                <li><strong>Found:</strong> Middle equals target → return index</li>
                <li><strong>Each step halves the search space → O(log n)!</strong></li>
            </ul>
        </div>


        <div class="visualization-section">
            <h3>🎬 Step-by-Step Visualization</h3>

            <div class="controls">
                <button class="btn btn-primary" id="stepBtn" onclick="step()">Step</button>
                <button class="btn btn-success" id="autoBtn" onclick="toggleAuto()">Auto Run</button>
                <button class="btn btn-warning" onclick="reset()">Reset</button>
            </div>

            <div class="info-box secondary" style="margin-bottom: 20px;">
                🎯 Target: <strong id="targetDisplay">9</strong>
            </div>

            <div class="status-message" id="statusMessage">
                Click "Step" or "Auto Run" to start visualization
            </div>

            <div class="variable-display">
                <div class="variable-box">
                    <div class="variable-name">Left</div>
                    <div class="variable-value" id="leftVal" style="color: #ff5722;">0</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">Right</div>
                    <div class="variable-value" id="rightVal" style="color: #3f51b5;">5</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">Mid</div>
                    <div class="variable-value" id="midVal" style="color: #4caf50;">-</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">nums[mid]</div>
                    <div class="variable-value" id="midNumVal">-</div>
                </div>
            </div>

            <div class="array-section">
                <div class="array-label">📥 Sorted Array:</div>
                <div class="array-container" id="arrayContainer"></div>
            </div>

            <div class="info-box" id="resultBox" style="display: none; margin-top: 20px;">
                Result will appear here
            </div>
        </div>

        <div class="code-section">
            <h3>💻 Python Solution</h3>
            <div class="code-block">
                <pre>from typing import List


"""
LeetCode Binary Search

Problem from LeetCode: https://leetcode.com/problems/binary-search/

Description:
Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

Example 1:
Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:
Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

Constraints:
1 &lt;= nums.length &lt;= 10^4
-10^4 &lt;= nums[i], target &lt;= 10^4
All the integers in nums are unique.
nums is sorted in ascending order.
"""

class Solution:

    def search(self, nums: List[int], target: int) -&gt;int:
        """
        Binary search implementation to find target in a sorted array.

        Args:
            nums: A sorted array of distinct integers
            target: The target value to search for

        Returns:
            int: The index of target if found, otherwise -1
        """
        left, right = 0, len(nums) - 1
        while left &lt;= right:
            mid = left + (right - left) // 2
            if nums[mid] == target:
                return mid
            elif nums[mid] &lt; target:
                left = mid + 1
            else:
                right = mid - 1
        return -1

    def search_recursive(self, nums: List[int], target: int) -&gt;int:
        """
        Recursive binary search implementation.

        Args:
            nums: A sorted array of distinct integers
            target: The target value to search for

        Returns:
            int: The index of target if found, otherwise -1
        """

        def binary_search(left, right):
            if left &gt; right:
                return -1
            mid = left + (right - left) // 2
            if nums[mid] == target:
                return mid
            elif nums[mid] &lt; target:
                return binary_search(mid + 1, right)
            else:
                return binary_search(left, mid - 1)
        return binary_search(0, len(nums) - 1)

    def search_bisect(self, nums: List[int], target: int) -&gt;int:
        """
        Binary search using Python's bisect module.

        Args:
            nums: A sorted array of distinct integers
            target: The target value to search for

        Returns:
            int: The index of target if found, otherwise -1
        """
        import bisect
        index = bisect.bisect_left(nums, target)
        if index &lt; len(nums) and nums[index] == target:
            return index
        else:
            return -1


if __name__ == '__main__':
    # Example usage based on LeetCode sample
    solution = Solution()

    # Example 1
    nums1 = [-1, 0, 3, 5, 9, 12]
    target1 = 9
    result1 = solution.search(nums1, target1)
    print(f"Example 1: {result1}")  # Expected: 4

    # Example 2
    nums2 = [-1, 0, 3, 5, 9, 12]
    target2 = 2
    result2 = solution.search(nums2, target2)
    print(f"Example 2: {result2}")  # Expected: -1

    # Test recursive method
    print("\nRecursive method:")
    result3 = solution.search_recursive(nums1, target1)
    print(f"Example 1: {result3}")  # Expected: 4

    # Test bisect method
    print("\nBisect method:")
    result4 = solution.search_bisect(nums1, target1)
    print(f"Example 1: {result4}")  # Expected: 4
</pre>
            </div>
        </div>
    </div>

    <script>
        const nums = [-1, 0, 3, 5, 9, 12];
        const target = 9;
        let left = 0;
        let right = nums.length - 1;
        let mid = -1;
        let found = false;
        let autoInterval = null;

        document.getElementById('targetDisplay').textContent = target;

        function init() {
            renderArray();
        }

        function renderArray() {
            const container = document.getElementById('arrayContainer');
            container.innerHTML = '';

            nums.forEach((num, idx) => {
                const box = document.createElement('div');
                box.className = 'array-box';
                box.id = `arr-${idx}`;
                box.innerHTML = `${num}<span class="index-label">[${idx}]</span>`;

                // Gray out elements outside current range
                if (idx < left || idx > right) {
                    box.style.background = '#e0e0e0';
                    box.style.opacity = '0.5';
                }

                // Highlight mid
                if (idx === mid) {
                    box.style.background = '#c8e6c9';
                    box.style.borderColor = '#4caf50';
                    box.style.borderWidth = '3px';
                }

                // Left pointer
                if (idx === left && idx !== mid) {
                    box.style.borderColor = '#ff5722';
                    box.style.borderWidth = '3px';
                }

                // Right pointer
                if (idx === right && idx !== mid) {
                    box.style.borderColor = '#3f51b5';
                    box.style.borderWidth = '3px';
                }

                // Found!
                if (found && idx === mid) {
                    box.classList.add('complete');
                }

                container.appendChild(box);
            });
        }

        function step() {
            if (found || left > right) {
                if (found) {
                    document.getElementById('statusMessage').className = 'status-message success';
                    document.getElementById('statusMessage').textContent = `✅ Found ${target} at index ${mid}!`;
                    document.getElementById('resultBox').style.display = 'block';
                    document.getElementById('resultBox').className = 'info-box secondary';
                    document.getElementById('resultBox').textContent = `Return ${mid}`;
                } else {
                    document.getElementById('statusMessage').className = 'status-message warning';
                    document.getElementById('statusMessage').textContent = `❌ ${target} not found in array!`;
                    document.getElementById('resultBox').style.display = 'block';
                    document.getElementById('resultBox').className = 'info-box highlight';
                    document.getElementById('resultBox').textContent = 'Return -1';
                }
                document.getElementById('stepBtn').disabled = true;
                stopAuto();
                return;
            }

            // Calculate mid
            mid = left + Math.floor((right - left) / 2);

            document.getElementById('leftVal').textContent = left;
            document.getElementById('rightVal').textContent = right;
            document.getElementById('midVal').textContent = mid;
            document.getElementById('midNumVal').textContent = nums[mid];

            if (nums[mid] === target) {
                found = true;
                document.getElementById('statusMessage').textContent =
                    `mid = ${mid}, nums[${mid}] = ${nums[mid]} = target. FOUND!`;
            } else if (nums[mid] < target) {
                document.getElementById('statusMessage').textContent =
                    `mid = ${mid}, nums[${mid}] = ${nums[mid]} < ${target}. Search right half (left = ${mid + 1})`;
                left = mid + 1;
            } else {
                document.getElementById('statusMessage').textContent =
                    `mid = ${mid}, nums[${mid}] = ${nums[mid]} > ${target}. Search left half (right = ${mid - 1})`;
                right = mid - 1;
            }

            renderArray();
        }

        function toggleAuto() {
            if (autoInterval) {
                stopAuto();
            } else {
                document.getElementById('autoBtn').textContent = 'Pause';
                autoInterval = setInterval(() => {
                    if (found || left > right) {
                        step();
                        stopAuto();
                    } else {
                        step();
                    }
                }, 1200);
            }
        }

        function stopAuto() {
            if (autoInterval) {
                clearInterval(autoInterval);
                autoInterval = null;
            }
            document.getElementById('autoBtn').textContent = 'Auto Run';
        }

        function reset() {
            stopAuto();
            left = 0;
            right = nums.length - 1;
            mid = -1;
            found = false;
            document.getElementById('stepBtn').disabled = false;
            document.getElementById('statusMessage').className = 'status-message';
            document.getElementById('statusMessage').textContent = 'Click "Step" or "Auto Run" to start visualization';
            document.getElementById('leftVal').textContent = '0';
            document.getElementById('rightVal').textContent = nums.length - 1;
            document.getElementById('midVal').textContent = '-';
            document.getElementById('midNumVal').textContent = '-';
            document.getElementById('resultBox').style.display = 'none';
            init();
        }

        init();
    </script>
</body>
</html>