75. Sort Colors --- one-pass algorithm --- leetcode算法笔记

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.

思路：遍历数组元素，遇到0往数组头部交换，遇到2往数组尾交换，1不做处理。

代码：

public void sortColors(int[] nums) {
int index1 = 0 ;
int index2 = nums.length - 1;
for(int i = 0 ; i <= index2 ;){
if(nums[i] == 0){
if(index1 < i){
nums[i] = nums[index1] ;
nums[index1] = 0 ;
}
index1 ++ ;
i ++ ;
}else if(nums[i] == 2){
while(i <= index2 && nums[index2] == 2) index2 -- ;
if(i < index2){
nums[i] = nums[index2] ;
nums[index2] = 2 ;
index2 -- ;
}
}else i++ ;
}
}

另一种平移插入法：

class Solution {
public:
void sortColors(int A[], int n) {
int i = -1;
int j = -1;
int k = -1;
for(int p = 0; p < n; p ++)
{
//根据第i个数字，挪动0~i-1串。
if(A[p] == 0)
{
A[++k] = 2; //2往后挪
A[++j] = 1; //1往后挪
A[++i] = 0; //0往后挪
}
else if(A[p] == 1)
{
A[++k] = 2;
A[++j] = 1;
}
else
A[++k] = 2;
}

}
};