907. 子数组的最小值之和
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最后更新于
输入：arr = [3,1,2,4]
输出：17
解释：
子数组为 [3]，[1]，[2]，[4]，[3,1]，[1,2]，[2,4]，[3,1,2]，[1,2,4]，[3,1,2,4]。
最小值为 3，1，2，4，1，1，2，1，1，1，和为 17。输入：arr = [11,81,94,43,3]
输出：444class Solution {
public:
int sumSubarrayMins(vector<int>& arr) {
int n = arr.size();
vector<int> monoStack;
vector<int> left(n), right(n);
for (int i = 0; i < n; i++ ) {
while(!monoStack.empty() && arr[i] <= arr[monoStack.back()]){
monoStack.pop_back();
}
left[i] = i - (monoStack.empty()? -1 : monoStack.back());
monoStack.emplace_back(i);
}
monoStack.clear();
for (int i = n -1; i >= 0; i--) {
while(!monoStack.empty() && arr[i] < arr[monoStack.back()]){
monoStack.pop_back();
}
right[i] = (monoStack.empty()? n : monoStack.back()) - i;
monoStack.emplace_back(i);
}
long long ans = 0;
long long MOD = 1e9+7;
for (int i =0; i < n; i++ ){
ans += (long long) left[i] * right[i] * arr[i];
ans %= MOD;
}
return ans;
}
};func sumSubarrayMins(arr []int) int {
n := len(arr)
monoStack := []int{}
left, right := make([]int, n), make([]int, n)
for i := 0; i < n; i++ {
for len(monoStack) > 0 && arr[i] <= arr[monoStack[len(monoStack)-1]] {
monoStack = monoStack[:len(monoStack)-1]
}
if len(monoStack) > 0 {
left[i] = i - monoStack[len(monoStack)-1]
}else {
left[i] = i + 1
}
monoStack = append(monoStack, i)
}
monoStack = []int{}
for i := n-1; i >= 0; i-- {
for len(monoStack) > 0 && arr[i] < arr[monoStack[len(monoStack)-1]] {
monoStack = monoStack[:len(monoStack)-1]
}
if len(monoStack) > 0 {
right[i] = monoStack[len(monoStack)-1] - i
}else {
right[i] = n - i
}
monoStack = append(monoStack, i)
}
ans := 0
for i := range left {
ans += left[i] * right[i] * arr[i]
ans %= 1e9 + 7
}
return ans
}