leetcode 3510

3510: 移除最小数对使数组有序Ⅱ

题干同 leetcode 3507

区别：（数据规模增大）

• 1 <= nums.length <= 50 (3507)
• -1000 <= nums[i] <= 1000

• 1 <= nums.length <= 105 (3510)
• -109 <= nums[i] <= 109

暴力模拟方法仅针对小数据范围，用于本题会超时。

思路：懒删除堆+数组模拟双向链表（详解见leetcode 3507）

class Solution {
public:
    int minimumPairRemoval(vector<int>& nums) {
        int n=nums.size();
        priority_queue<pair<long long,int>,vector<pair<long long,int>>,greater<>> pq;
        int dec=0;
        for(int i=0;i<n-1;i++){
            int x=nums[i],y=nums[i+1];
            if(x>y) dec++;
            pq.emplace(x+y,i);
        }
        vector<int> left(n+1),right(n);
        ranges::iota(left,-1);
        ranges::iota(right,1);

        vector<long long> a(nums.begin(),nums.end());
        int ans=0;
        while(dec){
            ans++;
            while(right[pq.top().second]>=n || pq.top().first!=a[pq.top().second]+a[right[pq.top().second]]){
                pq.pop();
            }
            auto[s,i]=pq.top();
            pq.pop();

            int nxt=right[i];
            dec-=a[i]>a[nxt];
            int pre=left[i];
            if(pre>=0){
                dec-=a[pre]>a[i];
                dec+=a[pre]>s;
                pq.emplace(a[pre]+s,pre);
            }
            int nxt2=right[nxt];
            if(nxt2<n){
                dec-=a[nxt]>a[nxt2];
                dec+=s>a[nxt2];
                pq.emplace(s+a[nxt2],i);
            }
            a[i]=s;
            int l=left[nxt],r=right[nxt];
            right[l]=r;
            left[r]=l;
            right[nxt]=n;
        }

        return ans;
    }
};