Leetcode: Sort Colors (4ms) (two pointers)

PROBLEM:

Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

Note:
You are not suppose to use the library's sort function for this problem.

click to show follow up.

See the figure below for two directional pointer method:

i0 points to 0 while i2 points to 2; i sweeps from left to right; note that i++ exist only when meets 0 or 1. 

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// codes

class Solution {

public:

       void sortColors(vector<int>& nums) {

              int i0 = 0, i2 = nums.size() - 1;

              for (int i = 0; i <= i2;){

                     if (nums[i] == 0){

                           swap(nums[i], nums[i0]);

                           ++i0;

                           continue;

                     }

                     else if (nums[i] == 2){

                           swap(nums[i], nums[i2]);

                           --i2;

                           continue;

                     }

                     ++i;

              }

       }

};