【九日集训】

1. 两个数对之间的最大乘积差

   int maxProductDifference(vector& nums) 
    {
        //------- 没有负数，直接排序
        int n = nums.size();
        sort(nums.begin(), nums.end());
        int a = nums[0],        b = nums[1];
        int c = nums[n-2],      d = nums[n-1];
        return c * d - a * b;
    }

2. 三角形的最大周长

 int largestPerimeter(vector& A) {
        sort(A.begin(), A.end());
        for (int i = (int)A.size() - 1; i >= 2; --i) {
            if (A[i - 2] + A[i - 1] > A[i]) {
                return A[i - 2] + A[i - 1] + A[i];
            }
        }
        return 0;
    }

3. 数组拆分 I

   public int arrayPairSum(int[] nums) {
        int n = nums.length;
        Arrays.sort(nums);
        int ans = 0;
        for (int i = 0; i < n; i += 2) ans += nums[i];
        return ans;
    }

4. 救生艇

int numRescueBoats(vector &people, int limit) {
        int ans = 0;
        sort(people.begin(), people.end());
        int light = 0, heavy = people.size() - 1;
        while (light <= heavy) {
            if (people[light] + people[heavy] > limit) {
                --heavy;
            } else {
                ++light;
                --heavy;
            }
            ++ans;
        }
        return ans;
    }

5. 摆动排序 II

void wiggleSort(vector& nums) {
        int length=nums.size();
        int bucket[5001]={0};
        for(int num:nums)   bucket[num]++;
        int big,small;
        if(length&1){
            big=length-2;
            small=length-1;
        }
        else{
            big=length-1;
            small=length-2;
        }
        int j=5000;
        //插入大数
        for(int i=1;i<=big;i+=2){
            while(bucket[j]==0) j--;
            nums[i]=j;
            bucket[j]--;
        }
        //插入小数
        for(int i=0;i<=small;i+=2){
            while(bucket[j]==0) j--;
            nums[i]=j;
            bucket[j]--;
        }
    }