leetcode_2909元素和最小的山形三元组

1. 题意

求 m i n ( a i + a j + a k ) , a j > a k , a j > a i , i < j < k min(a_i + a_j + a_k), a_j >a_k,a_j > a_i,i \lt j \lt k min(ai+aj+ak),aj>ak,aj>ai,i<j<k
元素和最小的山形三元组

2. 题解

枚举 j j j,求出 P r e M i n ( j − 1 ) PreMin(j - 1) PreMin(j−1)与 S u f M i n ( j + 1 ) SufMin(j +1) SufMin(j+1)

• 代码

class Solution {
public:
    int minimumSum(vector<int>& nums) {
        
        int sz = nums.size();

        vector<int> suf(sz);
        suf[sz - 1] = nums[sz - 1];
        for ( int i = sz - 2; ~i; --i ) {
            suf[i] = min(suf[i + 1], nums[i]);
        }

        int ans = -1;
        int pre = nums[0];
        for ( int i = 1; i < sz - 1; ++i ) {

            if ( nums[i] >　pre &&　nums[i] > suf[i + 1]) {
                int sum = nums[i] + pre + suf[i + 1];
                if ( ans == -1)
                    ans = sum;
                else
                    ans = min(ans, sum);
            }
            pre = min(pre, nums[i]);
        }

        return ans;
    }
};