513-Find-Bottom-Left-Tree-Value.java

class Solution {
    
    static class pair {
        TreeNode node;
        int level;
        pair(TreeNode node, int level) {
            this.node = node;
            this.level = level;
        }
    }
    
    public static int findBottomLeftValue(TreeNode root) {
        Queue<pair> q = new ArrayDeque<>();
        q.add(new pair(root, 0));
        pair ans = new pair(root, 0);
        while (!q.isEmpty()) {
            pair current = q.poll();
            TreeNode currentNode = current.node;
            int currentLevel = current.level;
            if (currentNode.left != null) q.add(new pair(currentNode.left, currentLevel + 1));
            if (currentNode.right != null) q.add(new pair(currentNode.right, currentLevel + 1));
            if (ans.level < currentLevel) ans = current;
        }
        return ans.node.val;
    }
}