add day seven

Author: libterty

README.md

@@ -7,3 +7,4 @@
     -   Day 4: [Number Complement](https://github.com/libterty/leetcode-challenge/blob/master/src/may/day-four/index.ts) :laughing:
     -   Day 5: [First Unique Character in a String](https://github.com/libterty/leetcode-challenge/blob/master/src/may/day-five/index.ts) :smirk:
     -   Day 6: [Majority Element](https://github.com/libterty/leetcode-challenge/blob/master/src/may/day-six/index.ts) :relaxed:
+    -   Day 7: [Cousins in Binary Tree](https://github.com/libterty/leetcode-challenge/blob/master/src/may/day-seven/index.ts) :hushed:

src/may/day-seven/index.ts

@@ -0,0 +1,51 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} x
+ * @param {number} y
+ * @return {boolean}
+ */
+
+interface Cache {
+    [key: number]: Child;
+}
+
+interface Child {
+    parent?: number;
+    depth: number;
+}
+
+export const isCousins = function (root, x, y): boolean {
+    const cache: Cache = {};
+
+    if (root && root.val) cache[root.val] = { parent: null, depth: 0 };
+
+    const dfs = (node, depth: number = 1): void => {
+        if (node && node.left) {
+            cache[node.left.val] = { parent: node.val, depth };
+            dfs(node.left, depth + 1);
+        }
+
+        if (node && node.right) {
+            cache[node.right.val] = { parent: node.val, depth };
+            dfs(node.right, depth + 1);
+        }
+    };
+
+    if (root) dfs(root);
+    else return false;
+
+    const depthOfx: number = cache[x].depth;
+    const depthOfy: number = cache[y].depth;
+    const parentOfx: number = cache[x].parent;
+    const parentOfy: number = cache[y].parent;
+
+    return depthOfx === depthOfy && parentOfx !== parentOfy;
+};