907. Sum of Subarray Minimums - medium
문제
Given an array of integers A, find the sum of min(B), where B ranges over every (contiguous) subarray of A.
Since the answer may be large, return the answer modulo 10^9 + 7.
제한사항
- 1 <= A.length <= 30000
- 1 <= A[i] <= 30000
입출력 예
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Input: [3,1,2,4]
Output: 17
Explanation: Subarrays are [3], [1], [2], [4], [3,1], [1,2], [2,4], [3,1,2], [1,2,4], [3,1,2,4].
Minimums are 3, 1, 2, 4, 1, 1, 2, 1, 1, 1. Sum is 17.
풀이
- Array, Stack
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// 분석 필요
class RepInteger{
public:
RepInteger(int v, int c) : val(v), count(c) {}
int val, count;
};
class Solution {
public:
int sumSubarrayMins(vector<int>& A) {
int ans = 0, dot = 0;
int n = A.size(), mod = 1e9 + 7;
stack<RepInteger> s;
for (int i = 0; i < n; ++i) {
// Add all answers for subarrays [i, j], i <= j
int count = 1;
while (!s.empty() && s.top().val >= A[i]) {
RepInteger node = s.top();
s.pop();
count += node.count;
dot -= node.val * node.count;
}
s.push(RepInteger(A[i], count));
dot += A[i] * count;
ans += dot;
ans %= mod;
}
return ans;
}
};