[LeetCode] 2347. Best Poker Hand

You are given an integer array ranks and a character array suits. You have 5 cards where the ith card has a rank of ranks[i] and a suit of suits[i].

The following are the types of poker hands you can make from best to worst:

1. "Flush": Five cards of the same suit.
2. "Three of a Kind": Three cards of the same rank.
3. "Pair": Two cards of the same rank.
4. "High Card": Any single card.

Return a string representing the best type of poker hand you can make with the given cards.

Note that the return values are case-sensitive.

Example 1:

Input: ranks = [13,2,3,1,9], suits = ["a","a","a","a","a"]
Output: "Flush"
Explanation: The hand with all the cards consists of 5 cards with the same suit, so we have a "Flush".

Example 2:

Input: ranks = [4,4,2,4,4], suits = ["d","a","a","b","c"]
Output: "Three of a Kind"
Explanation: The hand with the first, second, and fourth card consists of 3 cards with the same rank, so we have a "Three of a Kind".
Note that we could also make a "Pair" hand but "Three of a Kind" is a better hand.
Also note that other cards could be used to make the "Three of a Kind" hand.

Example 3:

Input: ranks = [10,10,2,12,9], suits = ["a","b","c","a","d"]
Output: "Pair"
Explanation: The hand with the first and second card consists of 2 cards with the same rank, so we have a "Pair".
Note that we cannot make a "Flush" or a "Three of a Kind".

Constraints:

• ranks.length == suits.length == 5
• 1 <= ranks[i] <= 13
• 'a' <= suits[i] <= 'd'
• No two cards have the same rank and suit.

最好的扑克手牌。

给你一个整数数组 ranks 和一个字符数组 suit 。你有 5 张扑克牌，第 i 张牌大小为 ranks[i] ，花色为 suits[i] 。

下述是从好到坏你可能持有的 手牌类型 ：

"Flush"：同花，五张相同花色的扑克牌。
"Three of a Kind"：三条，有 3 张大小相同的扑克牌。
"Pair"：对子，两张大小一样的扑克牌。
"High Card"：高牌，五张大小互不相同的扑克牌。
请你返回一个字符串，表示给定的 5 张牌中，你能组成的 最好手牌类型 。

注意：返回的字符串 大小写 需与题目描述相同。

来源：力扣（LeetCode）
链接：https://leetcode.cn/problems/best-poker-hand
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思路是 counting sort。

• 判断是不是同花，就是判断每张牌的花色是否跟第一张牌的花色一样，如果一样，即第一张牌花色的出现次数 == 牌的数量，则是同花
• 判断是不是三条和对子，则需要用 hashmap 记录每张数字不同的牌各自出现了几次，并且记录一个出现次数的最大值 max。如果 max >= 3，则说明有三条；如果 max == 2，则说明有对子
• 其余情况则只能是高牌

时间O(n)

空间O(n)

Java实现

class Solution {
    public String bestHand(int[] ranks, char[] suits) {
        int count = 0;
        char first = suits[0];
        for (char suit : suits) {
            if (suit == first) {
                count++;
            }
        }
        if (count == 5) {
            return "Flush";
        }

        HashMap<Integer, Integer> map = new HashMap<>();
        int max = 0;
        for (int r : ranks) {
            map.put(r, map.getOrDefault(r, 0) + 1);
            max = Math.max(max, map.get(r));
        }
        
        if (max >= 3) {
            return "Three of a Kind"; 
        } else if (max == 2) {
            return "Pair";
        }
        return "High Card";
    }
}

LeetCode 题目总结