```js
var displayTree = tree => console.log(JSON.stringify(tree, null, 2));
function Node(value) {
this.value = value;
this.left = null;
this.right = null;
}
function BinarySearchTree() {
this.root = null;
this.remove = function(value) {
if (this.root === null) {
return null;
}
var target;
var parent = null;
// find the target value and its parent
(function findValue(node = this.root) {
if (value == node.value) {
target = node;
} else if (value < node.value && node.left !== null) {
parent = node;
return findValue(node.left);
} else if (value < node.value && node.left === null) {
return null;
} else if (value > node.value && node.right !== null) {
parent = node;
return findValue(node.right);
} else {
return null;
}
}.bind(this)());
if (target === null) {
return null;
}
// count the children of the target to delete
var children =
(target.left !== null ? 1 : 0) + (target.right !== null ? 1 : 0);
// case 1: target has no children
if (children === 0) {
if (target == this.root) {
this.root = null;
} else {
if (parent.left == target) {
parent.left = null;
} else {
parent.right = null;
}
}
}
// case 2: target has one child
else if (children == 1) {
var newChild = target.left !== null ? target.left : target.right;
if (parent === null) {
target.value = newChild.value;
target.left = null;
target.right = null;
} else if (newChild.value < parent.value) {
parent.left = newChild;
} else {
parent.right = newChild;
}
target = null;
}
// case 3: target has two children, change code below this line
};
}
```
### After Tests
```js
BinarySearchTree.prototype = {
add: function(value) {
var node = this.root;
if (node == null) {
this.root = new Node(value);
return;
} else {
function searchTree(node) {
if (value < node.value) {
if (node.left == null) {
node.left = new Node(value);
return;
} else if (node.left != null) {
return searchTree(node.left);
}
} else if (value > node.value) {
if (node.right == null) {
node.right = new Node(value);
return;
} else if (node.right != null) {
return searchTree(node.right);
}
} else {
return null;
}
}
return searchTree(node);
}
},
inorder: function() {
if (this.root == null) {
return null;
} else {
var result = new Array();
function traverseInOrder(node) {
if (node.left != null) {
traverseInOrder(node.left);
}
result.push(node.value);
if (node.right != null) {
traverseInOrder(node.right);
}
}
traverseInOrder(this.root);
return result;
}
},
isBinarySearchTree() {
if (this.root == null) {
return null;
} else {
var check = true;
function checkTree(node) {
if (node.left != null) {
var left = node.left;
if (left.value > node.value) {
check = false;
} else {
checkTree(left);
}
}
if (node.right != null) {
var right = node.right;
if (right.value < node.value) {
check = false;
} else {
checkTree(right);
}
}
}
checkTree(this.root);
return check;
}
}
};
```
## Solution