Maximum Width of Binary Tree

题目
Given a binary tree, write a function to get the maximum width of the given tree. The width of a tree is the maximum width among all levels. The binary tree has the same structure as a full binary tree, but some nodes are null.

The width of one level is defined as the length between the end-nodes (the leftmost and right most non-null nodes in the level, where the null nodes between the end-nodes are also counted into the length calculation.

答案

public int widthOfBinaryTree(TreeNode root) {
        if(root == null) return 0;
        Queue<TreeNode> q = new LinkedList<TreeNode>();
        Map<TreeNode, Integer> map = new HashMap<>();
        int max = 1;
        
        q.offer(root);
        map.put(root, 0);
        while(q.size() != 0) {
            int curr_size = q.size();
            int leftmost = Integer.MAX_VALUE, rightmost = Integer.MIN_VALUE, idx;
            for(int i = 0; i < curr_size; i++) {
                TreeNode t = q.poll();
                if(t.left != null) {
                    q.offer(t.left);
                    idx = map.get(t) * 2 + 1;
                    map.put(t.left, idx);
                    leftmost = Math.min(leftmost, idx); 
                    rightmost = Math.max(rightmost, idx);
                    max = Math.max(max, rightmost - leftmost + 1);
                }
                if(t.right != null) {
                    q.offer(t.right);
                    idx = map.get(t) * 2 + 2;
                    map.put(t.right, idx);
                    leftmost = Math.min(leftmost, idx); 
                    rightmost = Math.max(rightmost, idx);
                    max = Math.max(max, rightmost - leftmost + 1);
                }
            }
            
        }
        return max;
    }