Breadth-First Search

1.Easy

(101)Symmetric Tree

(104)Maximum Depth of Binary Tree

(226)Invert Binary Tree

(617)Merge Two Binary Trees

2.Medium

(102)Binary Tree Level Order Traversal

(200)Number of Islands

(207)Course Schedule

(279)Perfect Squares

(322)Coin Change

(399)Evaluate Division

(494)Target Sum

3.Hard

(297)Serialize and Deserialize Binary Tree

(301)Remove Invalid Parentheses