README_EN.md

1711. Count Good Meals

中文文档

Description

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 to make a good meal.

Given an array of integers deliciousness where deliciousness[i] is the deliciousness of the i​​​​​​th​​​​​​​​ item of food, return the number of different good meals you can make from this list modulo 109 + 7.

Note that items with different indices are considered different even if they have the same deliciousness value.

 

Example 1:

Input: deliciousness = [1,3,5,7,9]
Output: 4
Explanation: The good meals are (1,3), (1,7), (3,5) and, (7,9).
Their respective sums are 4, 8, 8, and 16, all of which are powers of 2.

Example 2:

Input: deliciousness = [1,1,1,3,3,3,7]
Output: 15
Explanation: The good meals are (1,1) with 3 ways, (1,3) with 9 ways, and (1,7) with 3 ways.

 

Constraints:

• 1 <= deliciousness.length <= 105
• 0 <= deliciousness[i] <= 220

Solutions

Python3

class Solution:
    def countPairs(self, deliciousness: List[int]) -> int:
        mod = 10**9 + 7
        mx = max(deliciousness) << 1
        cnt = Counter()
        ans = 0
        for d in deliciousness:
            s = 1
            while s <= mx:
                ans = (ans + cnt[s - d]) % mod
                s <<= 1
            cnt[d] += 1
        return ans

class Solution:
    def countPairs(self, deliciousness: List[int]) -> int:
        mod = 10**9 + 7
        cnt = Counter(deliciousness)
        ans = 0
        for i in range(22):
            s = 1 << i
            for a, m in cnt.items():
                if (b := s - a) in cnt:
                    ans += m * (m - 1) if a == b else m * cnt[b]
        return (ans >> 1) % mod

Java

class Solution {
    private static final int MOD = (int) 1e9 + 7;

    public int countPairs(int[] deliciousness) {
        int mx = Arrays.stream(deliciousness).max().getAsInt() << 1;
        int ans = 0;
        Map<Integer, Integer> cnt = new HashMap<>();
        for (int d : deliciousness) {
            for (int s = 1; s <= mx; s <<= 1) {
                ans = (ans + cnt.getOrDefault(s - d, 0)) % MOD;
            }
            cnt.merge(d, 1, Integer::sum);
        }
        return ans;
    }
}

class Solution {
    private static final int MOD = (int) 1e9 + 7;

    public int countPairs(int[] deliciousness) {
        Map<Integer, Integer> cnt = new HashMap<>();
        for (int d : deliciousness) {
            cnt.put(d, cnt.getOrDefault(d, 0) + 1);
        }
        long ans = 0;
        for (int i = 0; i < 22; ++i) {
            int s = 1 << i;
            for (var x : cnt.entrySet()) {
                int a = x.getKey(), m = x.getValue();
                int b = s - a;
                if (!cnt.containsKey(b)) {
                    continue;
                }
                ans += 1L * m * (a == b ? m - 1 : cnt.get(b));
            }
        }
        ans >>= 1;
        return (int) (ans % MOD);
    }
}

C++

class Solution {
public:
    const int mod = 1e9 + 7;

    int countPairs(vector<int>& deliciousness) {
        int mx = *max_element(deliciousness.begin(), deliciousness.end()) << 1;
        unordered_map<int, int> cnt;
        int ans = 0;
        for (auto& d : deliciousness) {
            for (int s = 1; s <= mx; s <<= 1) {
                ans = (ans + cnt[s - d]) % mod;
            }
            ++cnt[d];
        }
        return ans;
    }
};

class Solution {
public:
    const int mod = 1e9 + 7;

    int countPairs(vector<int>& deliciousness) {
        unordered_map<int, int> cnt;
        for (int& d : deliciousness) ++cnt[d];
        long long ans = 0;
        for (int i = 0; i < 22; ++i) {
            int s = 1 << i;
            for (auto& [a, m] : cnt) {
                int b = s - a;
                if (!cnt.count(b)) continue;
                ans += 1ll * m * (a == b ? (m - 1) : cnt[b]);
            }
        }
        ans >>= 1;
        return ans % mod;
    }
};

Go

func countPairs(deliciousness []int) (ans int) {
	mx := 0
	for _, d := range deliciousness {
		mx = max(mx, d)
	}
	mx <<= 1
	const mod int = 1e9 + 7
	cnt := map[int]int{}
	for _, d := range deliciousness {
		for s := 1; s <= mx; s <<= 1 {
			ans = (ans + cnt[s-d]) % mod
		}
		cnt[d]++
	}
	return
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func countPairs(deliciousness []int) (ans int) {
    cnt := map[int]int{}
    for _, d := range deliciousness {
        cnt[d]++
    }
    const mod int = 1e9 + 7
    for i := 0; i < 22; i++ {
        s := 1 << i
        for a, m := range cnt {
            b := s - a
            if n, ok := cnt[b]; ok {
                if a == b {
                    ans += m * (m - 1)
                } else {
                    ans += m * n
                }
            }
        }
    }
    ans >>= 1
    return ans % mod
}

...