LintCode 143. Sort Colors II

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本文介绍了一种不使用标准库sort函数的颜色排序算法。该算法能在原地将包含K种不同颜色的对象数组按颜色升序排列。示例中给出了具体实现及测试代码。

This is a very interesting question! I like it!

#include <iostream>
#include <vector>
#include <climits>
using namespace std;

/*
  Given an array of n objects with K difference colors. sort them so that objects
  of the same color are adjacent, with the colors in the order 1, 2, ... k
  Note:
    You are not suppose to use the library's sort function for this problem.
  Exmaple:
  Given colors = [3, 2, 2, 1, 4], k = 4, you code should sort colors in-place to
  [1, 2, 2, 3, 4];
*/
void sortColorsII(vector<int>& colors, int k) {
  int start = 0;
  int end = colors.size() - 1;
  int count = 0;
  while(count < k) {
    int currMin = INT_MAX;
    int currMax = INT_MIN;
    for(int i = start; i <= end; ++i) {
      currMin = min(currMin, colors[i]);
      currMax = max(currMax, colors[i]);
    }
    int left = start;
    int right = end;
    int curr = left;
    while(curr <= right) {
      if(colors[curr] == currMin) {
        swap(colors[curr], colors[left]);
        curr++;
        left++;
      } else if(colors[curr] > currMin && colors[curr] < currMax) {
        curr++;
      } else {
        swap(colors[curr], colors[right]);
        right--;
      }
    }
    count += 2;
    start = left;
    end = right;
  }
}
int main(void) {
  vector<int> colors {3, 2, 2, 1, 4};
  sortColorsII(colors, 4);
  for(int i = 0; i < colors.size(); ++i) cout << colors[i] << endl;
}