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You are given an integer array nums and you have to return a new counts array. The counts array has the property where counts[i] is the number of smaller elements to the right of nums[i].
Example:
Given nums = [5, 2, 6, 1] To the right of 5 there are 2 smaller elements (2 and 1). To the right of 2 there is only 1 smaller element (1). To the right of 6 there is 1 smaller element (1). To the right of 1 there is 0 smaller element.
Return the array [2, 1, 1, 0]
1 class Solution { 2 public: 3 struct Node 4 { 5 int index; 6 int num; 7 Node(int a,int b) 8 { 9 index =a; 10 num =b; 11 } 12 }; 13 14 void mergesort(vector<Node>& nums,int start,int end,vector<int>&res) 15 { 16 17 if(start==end) 18 return; 19 if(start+1==end) 20 { 21 if(nums[start].num>nums[end].num) 22 { 23 Node tmp(1,1) ; 24 res[nums[start].index]++; 25 tmp = nums[start]; 26 nums[start] = nums[end]; 27 nums[end] = tmp; 28 return; 29 } 30 } 31 32 int middle = (start+end)/2; 33 mergesort(nums,start,middle,res); 34 mergesort(nums,middle+1,end,res); 35 36 int s1 = start; 37 int s2 = middle+1; 38 vector<int>right; 39 vector<Node> pac; 40 while(s1<=middle || s2<=end) 41 { 42 43 if(s1<=middle &&s2<=end) 44 { 45 if(nums[s1].num<=nums[s2].num) 46 { 47 pac.push_back(nums[s1]); 48 49 res[nums[s1].index]+=right.size(); 50 s1++; 51 } 52 else 53 { 54 pac.push_back(nums[s2]); 55 right.push_back(nums[s2].num); 56 s2++; 57 } 58 } 59 else if(s1<=middle) 60 { 61 pac.push_back(nums[s1]); 62 63 res[nums[s1].index]+=right.size(); 64 s1++; 65 } 66 else if(s2<=end) 67 { 68 pac.push_back(nums[s2]); 69 right.push_back(nums[s2].num); 70 s2++; 71 } 72 } 73 for(int i=start;i<=end;i++) 74 { 75 nums[i]=pac[i-start]; 76 } 77 78 } 79 vector<int> countSmaller(vector<int>& nums) { 80 81 int n = nums.size(); 82 vector<int>res; 83 vector<Node>nodes; 84 if(n==0) 85 return res; 86 res.resize(n,0); 87 for(int i=0;i<n;i++) 88 { 89 nodes.push_back(Node(i,nums[i])); 90 } 91 mergesort(nodes,0,n-1,res); 92 return res; 93 94 95 } 96 97 98 };
leetcode 315. Count of Smaller Numbers After Self
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原文地址：http://www.cnblogs.com/julyfrost/p/5445680.html
