题目:
题解:
class Solution {
private:
vector<int> c;
vector<int> a;
void Init(int length) {
c.resize(length, 0);
}
int LowBit(int x) {
return x & (-x);
}
void Update(int pos) {
while (pos < c.size()) {
c[pos] += 1;
pos += LowBit(pos);
}
}
int Query(int pos) {
int ret = 0;
while (pos > 0) {
ret += c[pos];
pos -= LowBit(pos);
}
return ret;
}
void Discretization(vector<int>& nums) {
a.assign(nums.begin(), nums.end());
sort(a.begin(), a.end());
a.erase(unique(a.begin(), a.end()), a.end());
}
int getId(int x) {
return lower_bound(a.begin(), a.end(), x) - a.begin() + 1;
}
public:
vector<int> countSmaller(vector<int>& nums) {
vector<int> resultList;
Discretization(nums);
Init(nums.size() + 5);
for (int i = (int)nums.size() - 1; i >= 0; --i) {
int id = getId(nums[i]);
resultList.push_back(Query(id - 1));
Update(id);
}
reverse(resultList.begin(), resultList.end());
return resultList;
}
};