LeetCode - Best Time to Buy and Sell Stock with Cooldown

25 Jan 2018 • LeetCode(Second)

Question Definition

Say you have an array for which the ith element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and sell one share of the stock multiple times) with the following restrictions:

You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again). After you sell your stock, you cannot buy stock on next day. (ie, cooldown 1 day)

More …

LeetCode - Predict the Winner

24 Jan 2018 • LeetCode(Second)

Question Definition

Given an array of scores that are non-negative integers. Player 1 picks one of the numbers from either end of the array followed by the player 2 and then player 1 and so on. Each time a player picks a number, that number will not be available for the next player. This continues until all the scores have been chosen. The player with the maximum score wins.

Given an array of scores, predict whether player 1 is the winner. You can assume each player plays to maximize his score.

Example 1:

Input: [1, 5, 2]
Output: False
Explanation: Initially, player 1 can choose between 1 and 2.
If he chooses 2 (or 1), then player 2 can choose from 1 (or 2) and 5. If player 2 chooses 5, then player 1 will be left with 1 (or 2).
So, final score of player 1 is 1 + 2 = 3, and player 2 is 5.
Hence, player 1 will never be the winner and you need to return False.

Example 2:

Input: [1, 5, 233, 7]
Output: True
Explanation: Player 1 first chooses 1. Then player 2 have to choose between 5 and 7. No matter which number player 2 choose, player 1 can choose 233.
Finally, player 1 has more score (234) than player 2 (12), so you need to return True representing player1 can win.

Note:

  1. 1 <= length of the array <= 20.
  2. Any scores in the given array are non-negative integers and will not exceed 10,000,000.
  3. If the scores of both players are equal, then player 1 is still the winner.

    Java Solution

    class Solution {
 public boolean PredictTheWinner(int[] nums) {
     int n = nums.length;
     int[][] dp = new int[n][n];
     for(int i = 0; i < dp.length; i++)
         for(int j = 0; j < dp.length; j++)
             dp[i][j] = -1;
     return canWin(nums, 0, n - 1, dp) >= 0;
 }
 private int canWin(int[] nums, int s, int e, int[][] dp) {
     if (dp[s][e] == -1) {
         dp[s][e] = (s == e) ? nums[s] : Math.max(nums[s] - canWin(nums, s + 1, e, dp), nums[e] - canWin(nums, s, e - 1, dp));
     }
     return dp[s][e];
 }
}

LeetCode - Palindromic Substrings

24 Jan 2018 • LeetCode(Second)

Question Definition

Given a string, your task is to count how many palindromic substrings in this string.

The substrings with different start indexes or end indexes are counted as different substrings even they consist of same characters.

More …