leetcode_c++:Divide and Conquer：Count of Smaller Numbers After Self（315）

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].

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].

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http://blog.csdn.net/murmured/article/details/50201147

struct Node {      int val;      int index;      int cnt;      Node(int val, int index) : val(val), index(index), cnt(0) {}      bool operator <= (const Node &node2)const {          return val <= node2.val;      }  };  class Solution {  public:      void combine(vector<Node> &nums, int Lpos, int Lend, int Rend, vector<Node> &temp) {          int Rpos = Lend + 1;          int Tpos = Lpos;          int n = Rend - Lpos + 1;          int t = Rpos;          while (Lpos <= Lend && Rpos <= Rend) {              if (nums[Lpos] <= nums[Rpos]) {                  temp[Tpos] = nums[Lpos];                  temp[Tpos].cnt += Rpos - t ;                  Tpos++; Lpos++;              }              else {                  temp[Tpos++] = nums[Rpos++];              }          }          while (Lpos <= Lend) {              temp[Tpos] = nums[Lpos];              temp[Tpos].cnt += Rpos - t;              Tpos++; Lpos++;          }          while (Rpos <= Rend)               temp[Tpos++] = nums[Rpos++];          for (int i = 0; i< n; i++, Rend--)               nums[Rend] = temp[Rend];      }      void merge_sort(vector<Node> & nums, int L, int R, vector<Node> &temp) {          if (L < R) {              int m = (L + R) >> 1;              merge_sort(nums, L, m, temp);              merge_sort(nums, m + 1, R, temp);              combine(nums, L, m, R, temp);          }      }      vector<int> countSmaller(vector<int>& nums) {          vector<Node> mynums;          vector<Node> temp(nums.size(), Node(0, 0));          for (int i = 0; i < nums.size(); i++)               mynums.push_back(Node(nums[i], i));          vector<int> ans(nums.size(), 0);          merge_sort(mynums, 0, nums.size() - 1, temp);          for (int i = 0; i < nums.size(); i++)               ans[mynums[i].index] = mynums[i].cnt;          return ans;      }  };