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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

  • 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);
     */
    
  • class FindSumPairs {
        private nums1: number[];
        private nums2: number[];
        private cnt: Map<number, number>;
    
        constructor(nums1: number[], nums2: number[]) {
            this.nums1 = nums1;
            this.nums2 = nums2;
            this.cnt = new Map();
            for (const x of nums2) {
                this.cnt.set(x, (this.cnt.get(x) || 0) + 1);
            }
        }
    
        add(index: number, val: number): void {
            const old = this.nums2[index];
            this.cnt.set(old, this.cnt.get(old)! - 1);
            this.nums2[index] += val;
            const now = this.nums2[index];
            this.cnt.set(now, (this.cnt.get(now) || 0) + 1);
        }
    
        count(tot: number): number {
            return this.nums1.reduce((acc, x) => acc + (this.cnt.get(tot - x) || 0), 0);
        }
    }
    
    /**
     * Your FindSumPairs object will be instantiated and called as such:
     * var obj = new FindSumPairs(nums1, nums2)
     * obj.add(index,val)
     * var param_2 = obj.count(tot)
     */
    
    
  • /**
     * @param {number[]} nums1
     * @param {number[]} nums2
     */
    var FindSumPairs = function (nums1, nums2) {
        this.nums1 = nums1;
        this.nums2 = nums2;
        this.cnt = new Map();
        for (const x of nums2) {
            this.cnt.set(x, (this.cnt.get(x) || 0) + 1);
        }
    };
    
    /**
     * @param {number} index
     * @param {number} val
     * @return {void}
     */
    FindSumPairs.prototype.add = function (index, val) {
        const old = this.nums2[index];
        this.cnt.set(old, this.cnt.get(old) - 1);
        this.nums2[index] += val;
        const now = this.nums2[index];
        this.cnt.set(now, (this.cnt.get(now) || 0) + 1);
    };
    
    /**
     * @param {number} tot
     * @return {number}
     */
    FindSumPairs.prototype.count = function (tot) {
        return this.nums1.reduce((acc, x) => acc + (this.cnt.get(tot - x) || 0), 0);
    };
    
    /**
     * Your FindSumPairs object will be instantiated and called as such:
     * var obj = new FindSumPairs(nums1, nums2)
     * obj.add(index,val)
     * var param_2 = obj.count(tot)
     */
    
    
  • public class FindSumPairs {
        private int[] nums1;
        private int[] nums2;
        private Dictionary<int, int> cnt = new Dictionary<int, int>();
    
        public FindSumPairs(int[] nums1, int[] nums2) {
            this.nums1 = nums1;
            this.nums2 = nums2;
            foreach (int x in nums2) {
                if (cnt.ContainsKey(x)) {
                    cnt[x]++;
                } else {
                    cnt[x] = 1;
                }
            }
        }
    
        public void Add(int index, int val) {
            int oldVal = nums2[index];
            if (cnt.TryGetValue(oldVal, out int oldCount)) {
                if (oldCount == 1) {
                    cnt.Remove(oldVal);
                } else {
                    cnt[oldVal] = oldCount - 1;
                }
            }
            nums2[index] += val;
            int newVal = nums2[index];
            if (cnt.TryGetValue(newVal, out int newCount)) {
                cnt[newVal] = newCount + 1;
            } else {
                cnt[newVal] = 1;
            }
        }
    
        public int Count(int tot) {
            int ans = 0;
            foreach (int x in nums1) {
                int target = tot - x;
                if (cnt.TryGetValue(target, out int count)) {
                    ans += count;
                }
            }
            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);
     */
    
    

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