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README.md

307. Range Sum Query - Mutable (Medium)

Given an integer array nums, handle multiple queries of the following types:

  1. Update the value of an element in nums.
  2. Calculate the sum of the elements of nums between indices left and right inclusive where left <= right.

Implement the NumArray class:

  • NumArray(int[] nums) Initializes the object with the integer array nums.
  • void update(int index, int val) Updates the value of nums[index] to be val.
  • int sumRange(int left, int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]).

 

Example 1:

Input
["NumArray", "sumRange", "update", "sumRange"]
[[[1, 3, 5]], [0, 2], [1, 2], [0, 2]]
Output
[null, 9, null, 8]

Explanation
NumArray numArray = new NumArray([1, 3, 5]);
numArray.sumRange(0, 2); // return 1 + 3 + 5 = 9
numArray.update(1, 2);   // nums = [1, 2, 5]
numArray.sumRange(0, 2); // return 1 + 2 + 5 = 8

 

Constraints:

  • 1 <= nums.length <= 3 * 104
  • -100 <= nums[i] <= 100
  • 0 <= index < nums.length
  • -100 <= val <= 100
  • 0 <= left <= right < nums.length
  • At most 3 * 104 calls will be made to update and sumRange.

Companies: Amazon, Google

Related Topics:
Array, Design, Binary Indexed Tree, Segment Tree

Similar Questions:

Solution 1. Prefix Sum + Dirty Bit

Use firstDirty to denote the smallest index of the updated number.

When doing sumRange, we calculate the prefix sum from firstDirty to nums.size() and reset firstDirty to be nums.size(), then return the prefix sum.

Next time if we sumRange without any update, we can directly return the prefix sum.

// OJ: https://leetcode.com/problems/range-sum-query-mutable/
// Author: github.com/lzl124631x
// Time:
//      NumArray: O(N)
//      update: O(1)
//      sumRange: O(N)
// Space: O(N)
class NumArray {
private:
    vector<int> sums;
    vector<int> nums;
    int firstDirty;
public:
    NumArray(vector<int> &nums) : sums(nums.size() + 1), nums(nums), firstDirty(0) {
    }

    void update(int i, int val) {
        nums[i] = val;
        firstDirty = min(firstDirty, i);
    }

    int sumRange(int i, int j) {
        if (firstDirty != nums.size()) {
            for (int i = firstDirty; i < nums.size(); ++i) {
                sums[i + 1] = sums[i] + nums[i];
            }
            firstDirty = nums.size();
        }
        return sums[j + 1] - sums[i];
    }
};

Solution 2. SQRT decomposition

// OJ: https://leetcode.com/problems/range-sum-query-mutable/
// Author: github.com/lzl124631x
// Time:
//      NumArray: O(N)
//      update: O(1)
//      sumRange: O(sqrt(N))
// Space: O(N)
// Ref: https://leetcode.com/problems/range-sum-query-mutable/solution/
class NumArray {
private:
    vector<int> sums;
    vector<int> nums;
    int len; // length of each section.
public:
    NumArray(vector<int> &nums) : nums(nums) {
        if (nums.empty()) return;
        len = ceil(sqrt(nums.size()));
        sums = vector<int>(ceil((double)nums.size() / len));
        for (int i = 0; i < nums.size(); ++i) {
            sums[i / len] += nums[i];
        }
    }

    void update(int i, int val) {
        sums[i / len] += val - nums[i];
        nums[i] = val;
    }

    int sumRange(int i, int j) {
        int sum = 0, start = i / len, end = j / len;
        if (start == end) {
            while (i <= j) sum += nums[i++];
        } else {
            for (int k = (start + 1) * len - 1; k >= i; --k) sum += nums[k];
            for (int k = start + 1; k < end; ++k) sum += sums[k];
            for (int k = end * len; k <= j; ++k) sum += nums[k];
        }
        return sum;
    }
};

Solution 3. Segment Tree

// OJ: https://leetcode.com/problems/range-sum-query-mutable/
// Author: github.com/lzl124631x
// Time: 
//      NumArray: O(N)
//      update: O(1)
//      sumRange: O(logN)
// Space: O(N)
class NumArray {
    vector<int> tree;
    int N;
    void buildTree(vector<int> &nums) {
        for (int i = 0, j = N; i < N;) tree[j++] = nums[i++];
        for (int i = N - 1; i > 0; --i) tree[i] = tree[2 * i] + tree[2 * i + 1];
    }
public:
    NumArray(vector<int>& nums) {
        if (nums.empty()) return;
        N = nums.size();
        tree = vector<int>(N * 2);
        buildTree(nums);
    }
    
    void update(int i, int val) {
        i += N;
        tree[i] = val;
        while (i > 0) {
            i /= 2;
            tree[i] = tree[2 * i] + tree[2 * i + 1];
        }
    }
    
    int sumRange(int i, int j) {
        i += N;
        j += N;
        int sum = 0;
        while (i <= j) {
            if (i % 2) sum += tree[i++];
            if (j % 2 == 0) sum += tree[j--];
            i /= 2;
            j /= 2;
        }
        return sum;
    }
};

Solution 4. Segment Tree with OOD

// OJ: https://leetcode.com/problems/range-sum-query-mutable/
// Author: github.com/lzl124631x
// Time: 
//      NumArray: O(N)
//      update: O(1)
//      sumRange: O(logN)
// Space: O(N
typedef int Merge(const int &a, const int& b);
class SegTree {
    vector<int> tree;
    int N;
    Merge *merge;
    void buildTree(vector<int> &nums) {
        for (int i = 0, j = N; i < N;) tree[j++] = nums[i++];
        for (int i = N - 1; i > 0; --i) tree[i] = merge(tree[2 * i], tree[2 * i + 1]);
    }
public:
    SegTree(vector<int> &nums, Merge merge) {
        N = nums.size();
        tree.resize(N * 2);
        this->merge = merge;
        buildTree(nums);
    }
    
    void update(int i, int val) {
        i += N;
        tree[i] = val;
        while (i > 0) {
            i /= 2;
            tree[i] = merge(tree[2 * i], tree[2 * i + 1]);
        }
    }
    
    int query(int from, int to, int def) {
        int i = from + N, j = to + N;
        int ans = def;
        while (i <= j) {
            if (i % 2) ans = merge(ans, tree[i++]);
            if (j % 2 == 0) ans = merge(ans, tree[j--]);
            i /= 2;
            j /= 2;
        }
        return ans;
    }
};
class NumArray {
    SegTree* tree;
public:
    NumArray(vector<int>& nums) {
        if (nums.empty()) return;
        tree = new SegTree(nums, [](const int &a, const int &b) { return a + b; });
    }
    void update(int i, int val) {
        tree->update(i, val);
    }
    int sumRange(int i, int j) {
        return tree->query(i, j, 0);
    }
};

Solution 5. Binary Indexed Tree

// OJ: https://leetcode.com/problems/range-sum-query-mutable/
// Author: github.com/lzl124631x
// Time: 
//      NumArray: O(N^2 * logN)
//      update: O(logN)
//      sumRange: O(logN)
// Ref: https://www.youtube.com/watch?v=WbafSgetDDk
class BIT {
    vector<int> A;
    static inline int lb(int x) { return x & -x; }
public:
    BIT(vector<int> nums) : A(nums.size() + 1) {
        for (int i = 0; i < nums.size(); ++i) {
            update(i + 1, nums[i]);
        }
    }
    int query(int i) {
        int ans = 0;
        for (; i; i -= lb(i)) ans += A[i];
        return ans;
    }
    int rangeQuery(int i, int j) { // i, j are inclusive
        return query(j) - query(i - 1);
    }
    void update(int i, int delta) {
        for (; i < A.size(); i += lb(i)) A[i] += delta;
    }
};
class NumArray {
    BIT tree;
    vector<int> A;
public:
    NumArray(vector<int>& A) : A(A), tree(A) {}
    void update(int index, int val) {
        tree.update(index + 1, val - A[index]);
        A[index] = val;
    }
    int sumRange(int left, int right) {
        return tree.rangeQuery(left + 1, right + 1);
    }
};