Thursday, August 6, 2020

976. Largest Perimeter Triangle ---------E ~~~~~

Q:

Given an array A of positive lengths, return the largest perimeter of a triangle with non-zero area, formed from 3 of these lengths.

If it is impossible to form any triangle of non-zero area, return 0.

 

    Example 1:

    Input: [2,1,2]
    Output: 5
    

    Example 2:

    Input: [1,2,1]
    Output: 0
    

    Example 3:

    Input: [3,2,3,4]
    Output: 10
    

    Example 4:

    Input: [3,6,2,3]
    Output: 8
    

     

    Note:

    1. 3 <= A.length <= 10000
    2. 1 <= A[i] <= 10^6

    A:

    首先 all permuation .  ------- 结果 LTE

    class Solution {
    public:
        int largestPerimeter(vector<int>& A) {
            int res = 0;
            int n = A.size();
            sort(A.begin(), A.end());
            for(int i =0;i<n; i++){
                for(int j = i+1;j<n;j++){
                    for(int k = j+1; k<n;k++){
                        if(A[i] + A[j] > A[k]){
                            res = max(res,  A[i] + A[j] + A[k] );
                        }
                    }
                }
            }
            return res;
        }
    };


    再研读题目,发现我们应该从打的数开始比较。  而且只需要比较某个数之前2个位置就够了

    class Solution {
    public:
        int largestPerimeter(vector<int>& A) {
            sort(A.begin(), A.end());
            for(int i =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;
        }
    };






    No comments:

    Post a Comment