[LeetCode] Find Bottom Left Tree Value

Find Bottom Left Tree Value

Given a binary tree, find the leftmost value in the last row of the tree.

BFS

Time Complexity
O(N)
Space Complexity
O(N)

思路

If you fully understand how bfs works, it is a really easy problem. Just add one line into the regular bfs template. if(i == 0) leftMost = cur;The leftmost will update until the last level.

代码

public int findBottomLeftValue(TreeNode root) {
    //corner case
    if(root == null) return 0;
    Queue<TreeNode> queue = new LinkedList<TreeNode>();
    queue.offer(root);
    TreeNode leftMost = null;
    while(!queue.isEmpty()){
        int size = queue.size();
        for(int i = 0; i < size; i++){
            TreeNode cur = queue.poll();
            if(i == 0) leftMost = cur;
            if(cur.left != null) queue.offer(cur.left);
            if(cur.right != null) queue.offer(cur.right);
        }
    }
    return leftMost.val;
}