LeetCode - Range Sum Query - Mutable

最新推荐文章于 2025-03-22 19:45:59 发布

real_lisa

最新推荐文章于 2025-03-22 19:45:59 发布

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本文介绍了一种数据结构NumArray的两种实现方式，用于高效处理数组的区间更新和区间求和操作。第一种方法使用前缀和数组进行区间查询优化，而第二种方法则通过分块策略进一步提高区间更新的效率。

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解法一

class NumArray {
public:
    NumArray(vector<int>& nums) {
        int s = 0;
        for(int n: nums){
            s += n;
            sums.push_back(s);
        }
    }
    
    void update(int i, int val) {
        int diff;
        if(i==0){
            diff = val-sums[0];
        }else{
            diff = val-(sums[i]-sums[i-1]);
        }
        for(int j=i;j<sums.size();j++){
            sums[j] += diff;
        }
    }
    
    int sumRange(int i, int j) {
        return i==0 ? sums[j] : sums[j]-sums[i-1];
    }
private:
    vector<int> sums;
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray* obj = new NumArray(nums);
 * obj->update(i,val);
 * int param_2 = obj->sumRange(i,j);
 */

解法二

class NumArray {
public:
    NumArray(vector<int>& nums) {
        if(nums.empty()) return;
        data=nums;
        len = ceil(sqrt(nums.size()));
        block.resize(len);
        for(int i=0;i<data.size();i++){
            block[i/len] += data[i];
        }
    }
    
    void update(int i, int val) {
        int diff = val-data[i];
        data[i] = val;
        block[i/len] += diff;
    }
    
    int sumRange(int i, int j) {
        int sum =0;
        int start=i/len, end=j/len;
        if(start==end){
            for(int k=i;k<=j;k++){
                sum += data[k];
            }
            return sum;
        }
        for(int k=i;k<(start+1)*len;k++){
            sum += data[k];
        }
        for(int k=start+1;k<end;k++){
            sum += block[k];
        }
        for(int k=end*len;k<=j;k++){
            sum += data[k];
        }
        return sum;
    }
private:
    int len;
    vector<int> data, block;
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray* obj = new NumArray(nums);
 * obj->update(i,val);
 * int param_2 = obj->sumRange(i,j);
 */