子数组的最小值之和

Leetcode题目链接

描述

详见中文题目链接。

解答

class Solution {
public:
    int sumSubarrayMins(vector<int>& arr) {
        const int MOD = 1e9 + 7;
        long res = 0L;
        stack<int> stk;
        for (int i = 0; i < arr.size(); i++) {
            while (!stk.empty() && arr[stk.top()] >= arr[i]) {
                int current = stk.top();
                stk.pop();
                int left = !stk.empty() ? stk.top() : -1;
                res += (current - left) * (i - current) * arr[current];
            }
            stk.push(i);
        }

        while (!stk.empty()) {
            int current = stk.top();
            stk.pop();
            int left = !stk.empty() ? stk.top() : -1;
            res += (current - left) * (arr.size() - current) * arr[current];
        }

        return res % MOD;
    }
};