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main2.cpp
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main2.cpp
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/// Source : https://leetcode.com/problems/maximum-segment-sum-after-removals/
/// Author : liuyubobobo
/// Time : 2022-08-20
#include <iostream>
#include <vector>
using namespace std;
/// Same idea with main.cpp, but has some optimization
/// Such as declare sum as a vector instead of map
/// ans no need to main sum_set but just just max_sum to keep the best result
///
/// Time Complexity: O(n)
/// Space Complexity: O(n)
class UF{
private:
vector<int> parent;
public:
UF(int n) : parent(n){
for(int i = 0 ; i < n ; i ++)
parent[i] = i;
}
int find(int p){
if(p != parent[p])
parent[p] = find(parent[p]);
return parent[p];
}
bool is_connected(int p, int q){
return find(p) == find(q);
}
void union_elements(int p, int q){
int p_root = find(p), q_root = find(q);
if(p_root == q_root) return;
parent[p_root] = q_root;
}
};
class Solution {
public:
vector<long long> maximumSegmentSum(vector<int>& nums, vector<int>& removeQueries) {
int n = nums.size();
vector<long long> v(n);
for(int i = 0; i < n; i ++) v[i] = nums[i];
for(int index: removeQueries) v[index] = 0;
UF uf(n);
vector<long long> sum(n, 0);
long long max_sum = 0;
for(int start = 0, i = 1; i <= n; i ++)
if(i == n || (v[i] != 0) != (v[start] != 0)){
if(v[start] != 0){
long long seg_sum = 0;
for(int j = start; j < i; j ++){
seg_sum += v[j];
uf.union_elements(start, j);
}
sum[uf.find(start)] = seg_sum;
max_sum = max(max_sum, seg_sum);
}
start = i;
}
vector<long long> res(n, max_sum);
for(int i = n - 1; i > 0; i --){
int index = removeQueries[i];
long long new_seg_sum = nums[index];
if(index - 1 >= 0 && v[index - 1] != 0){
long long left_sum = sum[uf.find(index - 1)];
new_seg_sum += left_sum;
uf.union_elements(index, index - 1);
}
if(index + 1 < n && v[index + 1] != 0){
long long right_sum = sum[uf.find(index + 1)];
new_seg_sum += right_sum;
uf.union_elements(index, index + 1);
}
sum[uf.find(index)] = new_seg_sum;
max_sum = max(max_sum, new_seg_sum);
res[i - 1] = max_sum;
v[index] = nums[index];
}
return res;
}
};
void print_vec(const vector<long long>& v){
for(long long e: v) cout << e << ' '; cout << '\n';
}
int main() {
vector<int> nums1 = {1, 2, 5, 6, 1};
vector<int> removeQueries1 = {0, 3, 2, 4, 1};
print_vec(Solution().maximumSegmentSum(nums1, removeQueries1));
// 14 7 2 2 0
return 0;
}