returns the number of left children in the tree. A left child is a node that appears as the root of the left-hand subtree of another node. An empty tree has 0 left nodes. For example, the following tree has four left children (the nodes storing the values 5, 1, 4, and 7):

return-left-children-tree.java

public int countLeftNodes() {
    return countLeftNodes(this.overallRoot);
}

private int countLeftNodes(IntTreeNode overallRoot) {
    if (overallRoot != null) {
        if (overallRoot.left != null) {
            return 1 + countLeftNodes(overallRoot.left) + countLeftNodes(overallRoot.right);
        } else {
            return countLeftNodes(overallRoot.right);
        }
    }
    return 0;
}