Create minimum-pair-removal-to-sort-array-i.cpp

Author: kamyu104

C++/minimum-pair-removal-to-sort-array-i.cpp

@@ -0,0 +1,53 @@
+// Time:  O(nlogn)
+// Space: O(n)
+
+// simulation, doubly linked list, bst
+class Solution {
+public:
+    int minimumPairRemoval(vector<int>& nums) {
+        vector<int64_t> arr(cbegin(nums), cend(nums));
+        vector<int> left(size(arr) + 1);
+        iota(begin(left), end(left), -1);
+        vector<int> right(size(arr));
+        iota(begin(right), end(right), 1);
+        int cnt = 0;
+        set<pair<int64_t, int>> bst;
+        const auto& add = [&](int i) {
+            if (0 <= i && i < right[i] && right[i] < size(arr)) {
+                bst.emplace(arr[i] + arr[right[i]], i);
+                if (arr[i] > arr[right[i]]) {
+                    ++cnt;
+                }
+            }
+        };
+
+        const auto& remove = [&](int i) {
+            if (0 <= i && i < right[i] && right[i] < size(arr)) {
+                bst.erase({arr[i] + arr[right[i]], i});
+                if (arr[i] > arr[right[i]]) {
+                    --cnt;
+                }
+            }
+        };
+
+        for (int i = 0; i + 1 < size(arr); ++i) {
+            bst.emplace(arr[i] + arr[i + 1], i);
+            if (arr[i] > arr[i + 1]) {
+                ++cnt;
+            }
+        }
+        int result = 0;
+        for (; cnt; ++result) {
+            const auto [_, i] = *cbegin(bst);
+            remove(left[i]);
+            remove(i);
+            remove(right[i]);
+            arr[i] += arr[right[i]];
+            left[right[right[i]]] = i;
+            right[i] = right[right[i]];
+            add(left[i]);
+            add(i);
+        }
+        return result;
+    }
+};