# 215. Kth Largest Element in an Array

Difficulty: Medium

Frequency: N/A

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

For example,
Given `[3,2,1,5,6,4]` and k = 2, return 5.

Note:
You may assume k is always valid, 1 ≤ k ≤ array’s length.

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```class Solution {
public:
int findKthLargest(vector<int>& nums, int k) {
priority_queue<int> q;
for (int n : nums) q.push(n);
for (int i = 1; i < k; i++) q.pop();
return q.top();
}
};
```

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# 240. Search a 2D Matrix II

Difficulty: Medium

Frequency: N/A

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

• Integers in each row are sorted in ascending from left to right.
• Integers in each column are sorted in ascending from top to bottom.

For example,

Consider the following matrix:

```[
[1,   4,  7, 11, 15],
[2,   5,  8, 12, 19],
[3,   6,  9, 16, 22],
[10, 13, 14, 17, 24],
[18, 21, 23, 26, 30]
]
```

Given target = `5`, return `true`.

Given target = `20`, return `false`.

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```class Solution {
public:
bool searchMatrix(vector<vector<int>>& matrix, int target) {
if (matrix.empty()) return false;
int m = matrix.size(), n = matrix[0].size();
int i = 0, j = n - 1;
while (i < m && j >= 0) {
if (matrix[i][j] == target) return true;
else if (matrix[i][j] < target) i++;
else j--;
}
return false;
}
};
```

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# 241. Different Ways to Add Parentheses

Difficulty: Medium

Frequency: N/A

Given a string of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. The valid operators are `+`,`-` and `*`.
Example 1Input: `"2-1-1"`.

```((2-1)-1) = 0
(2-(1-1)) = 2```

Output: `[0, 2]`
Example 2Input: `"2*3-4*5"`

```(2*(3-(4*5))) = -34
((2*3)-(4*5)) = -14
((2*(3-4))*5) = -10
(2*((3-4)*5)) = -10
(((2*3)-4)*5) = 10```

Output: `[-34, -14, -10, -10, 10]`

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```class Solution {
public:
vector<int> diffWaysToCompute(string input) {
vector<int> results;
for (int i = 0; i < input.size(); i++) {
char c = input[i];
if (!isdigit(c)) {
vector<int> left = diffWaysToCompute(input.substr(0, i));
vector<int> right = diffWaysToCompute(input.substr(i + 1));
for (int l : left) {
for (int r :right) {
switch(c) {
case '+': results.push_back(l + r); break;
case '-': results.push_back(l - r); break;
case '*': results.push_back(l * r); break;
}
}
}
}
}
if (results.empty()) results.push_back(stoi(input));
return results;
}
};
```

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