Create 1649.Create-Sorted-Array-through-Instructions_v1.cpp

Author: wisdompeak

Divide_Conquer/1649.Create-Sorted-Array-through-Instructions/1649.Create-Sorted-Array-through-Instructions_v1.cpp

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+class Solution {
+    int numSmaller[100005];
+    int temp[100005];    
+    int count[100005];
+    int nums[100005];
+    int sorted[100005];
+    int M = 1e9+7;
+public:
+    int createSortedArray(vector<int>& instructions) 
+    {
+        int n = instructions.size();
+        for (int i=0; i<n; i++)
+        {
+            nums[i] = instructions[i];
+            sorted[i] = instructions[i];
+        }            
+                
+        helper(0, n-1);        
+        int ret = 0;
+        for (int i=0; i<n; i++)
+        {
+            ret += min(numSmaller[i], i-count[nums[i]]-numSmaller[i]);
+            ret %= M;
+            count[nums[i]]++;
+        }            
+        return ret;
+    }
+    
+    void helper(int a, int b)
+    {
+        if (a>=b) return;        
+        int mid = a+(b-a)/2;
+        helper(a, mid);
+        helper(mid+1, b);
+        
+        for (int i=mid+1; i<=b; i++)
+        {
+            auto iter = lower_bound(sorted+a, sorted+mid+1, nums[i]);
+            numSmaller[i] += iter-(sorted+a);
+        }
+           
+        int i=a, j=mid+1, p = 0;        
+        while (i<=mid && j<=b)
+        {
+            if (sorted[i]<=sorted[j])
+            {
+                temp[p] = sorted[i];
+                i++;
+            }                
+            else
+            {
+                temp[p] = sorted[j];
+                j++;
+            } 
+            p++;
+        }
+        while (i<=mid)
+        {
+            temp[p] = sorted[i];
+            i++;
+            p++;
+        }
+        while (j<=b)
+        {
+            temp[p] = sorted[j];
+            j++;
+            p++;
+        }
+        for (int i=0; i<b-a+1; i++)
+            sorted[a+i] = temp[i];
+    }
+};