LeetCode - Accounts Merge

26 Dec 2017 • LeetCode

Question Definition

Given a list accounts, each element accounts[i] is a list of strings, where the first element accounts[i][0] is a name, and the rest of the elements are emails representing emails of the account.

Now, we would like to merge these accounts. Two accounts definitely belong to the same person if there is some email that is common to both accounts. Note that even if two accounts have the same name, they may belong to different people as people could have the same name. A person can have any number of accounts initially, but all of their accounts definitely have the same name.

After merging the accounts, return the accounts in the following format: the first element of each account is the name, and the rest of the elements are emails in sorted order. The accounts themselves can be returned in any order.

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LeetCode - Populating Next Right Pointers in Each Node II

25 Dec 2017 • LeetCode

Question Definition

Follow up for problem “Populating Next Right Pointers in Each Node”.

What if the given tree could be any binary tree? Would your previous solution still work?

Note:

  • You may only use constant extra space.

For example, Given the following binary tree,

         1
       /  \
      2    3
     / \    \
    4   5    7

After calling your function, the tree should look like:

         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \    \
    4-> 5 -> 7 -> NULL

Java Solution

public void connect(TreeLinkNode root) {
    TreeLinkNode dummy = new TreeLinkNode(0);
    TreeLinkNode t = dummy;
    while (root != null) {
        if (root.left != null) {
            t.next = root.left;
            t = t.next;
        }
        if (root.right != null) {
            t.next = root.right;
            t = t.next;
        }
        root = root.next;
        if (root == null) {
            t = dummy;
            root = dummy.next;
            dummy.next = null;
        }
    }
}

LeetCode - Network Delay Time

25 Dec 2017 • LeetCode

Question Definition

There are N network nodes, labelled 1 to N.

Given times, a list of travel times as directed edges times[i] = (u, v, w), where u is the source node, v is the target node, and w is the time it takes for a signal to travel from source to target.

Now, we send a signal from a certain node K. How long will it take for all nodes to receive the signal? If it is impossible, return -1.

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