leetcode_2909元素和最小的山形三元组

1. 题意

求 $min(a_i+a_j+a_k),a_j>a_k,a_j>a_i,i<j<k$
元素和最小的山形三元组

2. 题解

枚举$j$,求出$PreMin(j-1)$与$SufMin(j+1)$

• 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;
    }
};
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