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1865. Finding Pairs With a Certain Sum

Description

You are given two integer arrays nums1 and nums2. You are tasked to implement a data structure that supports queries of two types:

1. Add a positive integer to an element of a given index in the array nums2.
2. Count the number of pairs (i, j) such that nums1[i] + nums2[j] equals a given value (0 <= i < nums1.length and 0 <= j < nums2.length).

Implement the FindSumPairs class:

• FindSumPairs(int[] nums1, int[] nums2) Initializes the FindSumPairs object with two integer arrays nums1 and nums2.
• void add(int index, int val) Adds val to nums2[index], i.e., apply nums2[index] += val.
• int count(int tot) Returns the number of pairs (i, j) such that nums1[i] + nums2[j] == tot.

 

Example 1:

Input
["FindSumPairs", "count", "add", "count", "count", "add", "add", "count"]
[[[1, 1, 2, 2, 2, 3], [1, 4, 5, 2, 5, 4]], [7], [3, 2], [8], [4], [0, 1], [1, 1], [7]]
Output
[null, 8, null, 2, 1, null, null, 11]

Explanation
FindSumPairs findSumPairs = new FindSumPairs([1, 1, 2, 2, 2, 3], [1, 4, 5, 2, 5, 4]);
findSumPairs.count(7);  // return 8; pairs (2,2), (3,2), (4,2), (2,4), (3,4), (4,4) make 2 + 5 and pairs (5,1), (5,5) make 3 + 4
findSumPairs.add(3, 2); // now nums2 = [1,4,5,4,5,4]
findSumPairs.count(8);  // return 2; pairs (5,2), (5,4) make 3 + 5
findSumPairs.count(4);  // return 1; pair (5,0) makes 3 + 1
findSumPairs.add(0, 1); // now nums2 = [2,4,5,4,5,4]
findSumPairs.add(1, 1); // now nums2 = [2,5,5,4,5,4]
findSumPairs.count(7);  // return 11; pairs (2,1), (2,2), (2,4), (3,1), (3,2), (3,4), (4,1), (4,2), (4,4) make 2 + 5 and pairs (5,3), (5,5) make 3 + 4

 

Constraints:

• 1 <= nums1.length <= 1000
• 1 <= nums2.length <= 105
• 1 <= nums1[i] <= 109
• 1 <= nums2[i] <= 105
• 0 <= index < nums2.length
• 1 <= val <= 105
• 1 <= tot <= 109
• At most 1000 calls are made to add and count each.

Solutions

• Java
• C++
• Python
• Go

• class FindSumPairs {
      private int[] nums1;
      private int[] nums2;
      private Map<Integer, Integer> cnt = new HashMap<>();
  
      public FindSumPairs(int[] nums1, int[] nums2) {
          this.nums1 = nums1;
          this.nums2 = nums2;
          for (int v : nums2) {
              cnt.put(v, cnt.getOrDefault(v, 0) + 1);
          }
      }
  
      public void add(int index, int val) {
          int old = nums2[index];
          cnt.put(old, cnt.get(old) - 1);
          cnt.put(old + val, cnt.getOrDefault(old + val, 0) + 1);
          nums2[index] += val;
      }
  
      public int count(int tot) {
          int ans = 0;
          for (int v : nums1) {
              ans += cnt.getOrDefault(tot - v, 0);
          }
          return ans;
      }
  }
  
  /**
   * Your FindSumPairs object will be instantiated and called as such:
   * FindSumPairs obj = new FindSumPairs(nums1, nums2);
   * obj.add(index,val);
   * int param_2 = obj.count(tot);
   */
  

• class FindSumPairs {
  public:
      FindSumPairs(vector<int>& nums1, vector<int>& nums2) {
          this->nums1 = nums1;
          this->nums2 = nums2;
          for (int& v : nums2) {
              ++cnt[v];
          }
      }
  
      void add(int index, int val) {
          int old = nums2[index];
          --cnt[old];
          ++cnt[old + val];
          nums2[index] += val;
      }
  
      int count(int tot) {
          int ans = 0;
          for (int& v : nums1) {
              ans += cnt[tot - v];
          }
          return ans;
      }
  
  private:
      vector<int> nums1;
      vector<int> nums2;
      unordered_map<int, int> cnt;
  };
  
  /**
   * Your FindSumPairs object will be instantiated and called as such:
   * FindSumPairs* obj = new FindSumPairs(nums1, nums2);
   * obj->add(index,val);
   * int param_2 = obj->count(tot);
   */
  

• class FindSumPairs:
      def __init__(self, nums1: List[int], nums2: List[int]):
          self.nums1 = nums1
          self.nums2 = nums2
          self.cnt = Counter(nums2)
  
      def add(self, index: int, val: int) -> None:
          old = self.nums2[index]
          self.cnt[old] -= 1
          self.cnt[old + val] += 1
          self.nums2[index] += val
  
      def count(self, tot: int) -> int:
          return sum(self.cnt[tot - v] for v in self.nums1)
  
  
  # Your FindSumPairs object will be instantiated and called as such:
  # obj = FindSumPairs(nums1, nums2)
  # obj.add(index,val)
  # param_2 = obj.count(tot)
  
  

• type FindSumPairs struct {
  	nums1 []int
  	nums2 []int
  	cnt   map[int]int
  }
  
  func Constructor(nums1 []int, nums2 []int) FindSumPairs {
  	cnt := map[int]int{}
  	for _, v := range nums2 {
  		cnt[v]++
  	}
  	return FindSumPairs{nums1, nums2, cnt}
  }
  
  func (this *FindSumPairs) Add(index int, val int) {
  	old := this.nums2[index]
  	this.cnt[old]--
  	this.cnt[old+val]++
  	this.nums2[index] += val
  }
  
  func (this *FindSumPairs) Count(tot int) (ans int) {
  	for _, v := range this.nums1 {
  		ans += this.cnt[tot-v]
  	}
  	return
  }
  
  /**
   * Your FindSumPairs object will be instantiated and called as such:
   * obj := Constructor(nums1, nums2);
   * obj.Add(index,val);
   * param_2 := obj.Count(tot);
   */
  

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