75. 颜色分类

75. 颜色分类

双指针——快慢指针

class Solution {
    public void sortColors(int[] nums) {
        int n = nums.length;

        int p0 = 0;
        for(int i = 0; i < n; i++){
            if(nums[i] == 0){
                swap(nums, p0, i);
                p0++;
            }
        }

        int p1 = p0;
        for(int i = p0; i < n; i++){
            if(nums[i] == 1){
                swap(nums, p1, i);
                p1++;
            }
        }
    }

    void swap(int[] nums, int x, int y){
        int tmp = nums[x];
        nums[x] = nums[y];
        nums[y] = tmp;
    }
}

一次遍历

class Solution {
    public void sortColors(int[] nums) {
        int n = nums.length;
        int p0 = 0, p2 = n - 1;

        for(int i = 0; i < n; i++){
            while(i < p2 && nums[i] == 2){
                swap(nums, p2, i);
                p2--;
            }
            if(nums[i] == 0){
                swap(nums, p0, i);
                p0++;
            }
        }
    }

    void swap(int[] nums, int x, int y){
        int tmp = nums[x];
        nums[x] = nums[y];
        nums[y] = tmp;
    }
}