1.颜色分类

颜色分类

class Solution {
public:void sortColors(vector<int>& nums) {int n = nums.size();int left = -1,right=n,i=0;while(i<right){if(nums[i] == 0) swap(nums[++left],nums[i++]);else if(nums[i] == 1) i++;else swap(nums[--right],nums[i]);}}
};

2.排序数组

排序数组

class Solution {
public:vector<int> sortArray(vector<int>& nums) {srand(time(NULL));//种下一颗随机种子qsort(nums,0,nums.size()-1);return nums;}void qsort(vector<int>& nums,int l,int r){if(l>=r) return;int left = l-1,right = r+1,i=l;int key = getRandom(nums,l,r);while(i<right){if(nums[i]<key) swap(nums[++left],nums[i++]);else if(nums[i] == key) i++;else swap(nums[--right],nums[i]);}//[l,left] [left+1,right-1] [right,r]qsort(nums,l,left);qsort(nums,right,r);}//等概率获取区间内的任何数据int getRandom(vector<int>& nums,int left,int right){return nums[rand()%(right-left+1)+left];}
};

3.数组中的第k个最大元素

数组中的第k个最大元素

class Solution {
public:int findKthLargest(vector<int>& nums, int k) {srand(time(NULL));return qsort(nums,0,nums.size()-1,k);}int qsort(vector<int>& nums,int l,int r,int k){if(l==r) return nums[l];//1.随机选择基准元素int left = l-1,right=r+1,i=l;int key = nums[rand()%(r-l+1)+l];while(i<right){if(nums[i]<key) swap(nums[++left],nums[i++]);else if(nums[i] == key) i++;else swap(nums[--right],nums[i]);}//2.分情况讨论//[l,left][left+1,right-1][right,r]int c = r-right+1,b=right-left-1;if(c>=k) return qsort(nums,right,r,k);else if(b+c>=k) return key;else return qsort(nums,l,left,k-b-c);}
};

4.最小的k个数

最小的k个数

class Solution {
public:vector<int> smallestK(vector<int>& arr, int k) {srand(time(NULL));qsort(arr,0,arr.size()-1,k);return {arr.begin(),arr.begin()+k};}void qsort(vector<int>& arr,int l,int r,int k){if(l>=r) return;int left = l-1,right=r+1,i=l;int key = getRandom(arr,l,r);while(i<right){if(arr[i]<key) swap(arr[++left],arr[i++]);else if(arr[i] == key) i++;else swap(arr[--right],arr[i]);}//[l,left][left+1,right-1][right,r]int a = left-l+1,b = right-left-1;if(a>k) qsort(arr,l,left,k);else if(a+b>=k) return;else qsort(arr,right,r,k-a-b);}int getRandom(vector<int>& arr,int left,int right){return arr[rand()%(right-left+1)+left];}
};