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Concept

Introduction

Level by level with a FIFO queue
step 1 / 17
binary tree
4
2
5
1
6
3
7
queue (FIFO)
front →
(empty)
← back
Concept
▸
1bfs(root):
2    queue = [root]
3    while queue not empty:
4        node = queue.dequeue()   // front
5        if node is leaf: continue
6        enqueue node.children     // back
7    // visits nodes level by level
state
  • orderlevel by level

line 1Breadth-First Search explores a tree LEVEL BY LEVEL — all depth-1 nodes, then all depth-2, and so on. The engine is a QUEUE (first-in, first-out): you take a node from the FRONT, and add its children to the BACK. Contrast DFS, which used a stack and plunged deep first.