Tree Diameter

@interface TreeNode: NSObject
@property (nonatomic) TreeNode* left;
@property (nonatomic) TreeNode* right;
@property (nonatomic) id data;
@end

@implementation TreeNode
@end

@interface Solution: NSObject
-(int)treeDiameter:(TreeNode *)root;
@end

@implementation Solution
-(int)treeDiameter:(TreeNode *)root {
    int d = 0;
    [self pfx_deepestChild:root mostDiameter:&d];
    return d;
}

-(int)pfx_deepestChild:(TreeNode *)root mostDiameter:(int *)diameter {
    if(!root) return 0;

    int deepestLeft = 0;
    int deepestRight = 0;
    if(root.left) deepestLeft = [self pfx_deepestChild:root.left mostDiameter:diameter];
    if(root.right) deepestRight = [self pfx_deepestChild:root.left mostDiameter:diameter];

    int localDiameter = deepestLeft + deepestRight + 1;
    *diameter = MAX(localDiameter, *diameter);

    return MAX(deepestLeft, deepestRight) + 1;
}
@end