Stream Watcher: First Unique Hero

📋 OBJECTIVE

Find the first non-repeating character in a stream. As new characters arrive, track which character appears only once and comes first!

📝 ALGORITHM

// Data structures
freqMap = {}  // char → count
queue = []    // candidates

function processChar(c) {
  // Update frequency
  freqMap[c]++;
  
  // Add to queue if first time
  if (freqMap[c] == 1) {
    queue.push(c);
  }
  
  // Remove invalid fronts
  while (queue.length > 0 
         && freqMap[queue[0]] > 1) {
    queue.shift();
  }
  
  // First unique = front
  return queue[0] || "-1";
}

💡 INSIGHT

The queue holds potential unique characters. We lazily remove from front when they become repeated. O(1) amortized per character!

📺 STREAM MONITOR Click characters to add to stream!

Add to stream:

First Non-Repeating: -

📥 INPUT STREAM

Stream empty...

📥 CANDIDATES QUEUE

No candidates...

📊 FREQUENCY MAP

Empty map...

👁️ STREAM WATCHER

Success!