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Brush questions in summer -day3
2022-07-06 03:21:00 【Small grey QAQ】
1.303. Area and retrieval - The array is immutable
class NumArray {
public:
vector<int> sums;
NumArray(vector<int>& nums) {
int n = nums.size();
sums.resize(n + 1);
for (int i = 0; i < n; i++) {
sums[i + 1] = sums[i] + nums[i];
}
}
int sumRange(int i, int j) {
return sums[j + 1] - sums[i];
}
};
2.1588. The sum of all odd length subarrays
class Solution {
public:
int sumOddLengthSubarrays(vector<int>& arr) {
int sum = 0;
int n = arr.size();
for (int start = 0; start < n; start++) {
for (int length = 1; start + length <= n; length += 2) {
int end = start + length - 1;
for (int i = start; i <= end; i++) {
sum += arr[i];
}
}
}
return sum;
}
};
3.930. And the same binary subarray
class Solution {
public:
int numSubarraysWithSum(vector<int>& nums, int goal) {
int sum = 0;
unordered_map<int, int> cnt;
int ret = 0;
for (auto& num : nums) {
cnt[sum]++;
sum += num;
ret += cnt[sum - goal];
}
return ret;
}
};
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