{"id":7893,"date":"2021-01-02T23:35:38","date_gmt":"2021-01-03T07:35:38","guid":{"rendered":"https:\/\/zxi.mytechroad.com\/blog\/?p=7893"},"modified":"2021-01-02T23:37:34","modified_gmt":"2021-01-03T07:37:34","slug":"leetcode-1711-count-good-meals","status":"publish","type":"post","link":"https:\/\/zxi.mytechroad.com\/blog\/hashtable\/leetcode-1711-count-good-meals\/","title":{"rendered":"\u82b1\u82b1\u9171 LeetCode 1711. Count Good Meals"},"content":{"rendered":"\n

A good meal<\/strong> is a meal that contains exactly two different food items<\/strong> with a sum of deliciousness equal to a power of two.<\/p>\n\n\n\n

You can pick any<\/strong> two different foods to make a good meal.<\/p>\n\n\n\n

Given an array of integers deliciousness<\/code> where deliciousness[i]<\/code> is the deliciousness of the i\u200b\u200b\u200b\u200b\u200b\u200bth<\/sup>\u200b\u200b\u200b\u200b<\/code>\u200b\u200b\u200b\u200b item of food, return the number of different good meals<\/strong> you can make from this list modulo<\/em> 109<\/sup> + 7<\/code>.<\/p>\n\n\n\n

Note that items with different indices are considered different even if they have the same deliciousness value.<\/p>\n\n\n\n

Example 1:<\/strong><\/p>\n\n\n\n

Input:<\/strong> deliciousness = [1,3,5,7,9]\nOutput:<\/strong> 4\nExplanation: <\/strong>The good meals are (1,3), (1,7), (3,5) and, (7,9).\nTheir respective sums are 4, 8, 8, and 16, all of which are powers of 2.\n<\/pre>\n\n\n\n
Example 2:<\/strong><\/p>\n\n\n\n
Input:<\/strong> deliciousness = [1,1,1,3,3,3,7]\nOutput:<\/strong> 15\nExplanation: <\/strong>The good meals are (1,1) with 3 ways, (1,3) with 9 ways, and (1,7) with 3 ways.<\/pre>\n\n\n\n
Constraints:<\/strong><\/p>\n\n\n\n
  • 1 <= deliciousness.length <= 105<\/sup><\/code><\/li>
  • 0 <= deliciousness[i] <= 220<\/sup><\/code><\/li><\/ul>\n\n\n\n
    Solution: Hashtable<\/strong><\/h2>\n\n\n\n
    Same idea as LeetCode 1: Two Sum<\/p>\n\n\n\n
    Use a hashtable to store the occurrences of all the numbers added so far. For a  new number x, check all possible 2^i – x. ans += freq[2^i – x] 0 <= i <= 21<\/p>\n\n\n\n
    Time complexity: O(22n)
    Space complexity: O(n)<\/p>\n\n\n\n
    \n
    C++<\/h2>\n
    \n\n
    \nclass Solution {\npublic:\n  int countPairs(vector& A) {\n    constexpr int kMod = 1e9 + 7;\n    unordered_map m;    \n    long ans = 0;\n    for (int x : A) {\n      for (int t = 1; t <= 1 << 21; t *= 2) {\n        auto it = m.find(t - x);\n        if (it != end(m)) ans += it->second;\n      }\n      ++m[x];\n    }\n    return ans % kMod;\n  }\n};\n<\/pre>\n\n<\/div>
    Python3<\/h2>\n
    \n\n
    \nclass Solution:\n  def countPairs(self, deliciousness: List[int]) -> int:\n    sums = [1<\n<\/div><\/div>\n","protected":false},"excerpt":{"rendered":"
    A good meal is a meal that contains exactly two different food items with a sum of deliciousness equal to a power of two. You can pick any two different foods…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[70],"tags":[82,177,269,492,208],"class_list":["post-7893","post","type-post","status-publish","format-standard","hentry","category-hashtable","tag-hashtable","tag-medium","tag-pairs","tag-target-sum","tag-two-sum","entry","simple"],"_links":{"self":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/7893","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/comments?post=7893"}],"version-history":[{"count":3,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/7893\/revisions"}],"predecessor-version":[{"id":7896,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/7893\/revisions\/7896"}],"wp:attachment":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/media?parent=7893"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/categories?post=7893"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/tags?post=7893"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}