Solving Range Sum Query - Mutable
class NumArray { public: NumArray(vector<int> nums) { Image.push_back(vector<int>(nums)); int size = nums.size(); int level = 1; while(size >= 10) { Image.push_back(vector<int>(size/10, 0)); for(int i = 0; i < size/10; i++) { int localSum = 0; for(int j = 0; j < 10; j++) localSum += Image[level-1][10*i+j]; Image[level][i] = localSum; } size /= 10; level += 1; } } void update(int i, int val) { int diff = val - Image[0][i]; Image[0][i] = val; for(int level = 1; level < Image.size(); level++) { i /= 10; Image[level][i] += diff; } } int sumRange(int i, int j) { if(i == j) return Image[0][i];