Coding Interviews

Number of Submatrices That Sum to Target

Leetcode 1074: Number of Submatrices That Sum to Target

CATEGORY: HARD Problem Given a matrix and a target, return the number of non-empty submatrices that sum to target. A submatrix x1, y1, x2, y2 is the set of all cells matrix[x][y] with x1 <= x <= x2 and y1 <= y <= y2. Two submatrices (x1, y1, x2, y2) and (x1′, y1′, x2′, y2′) are different if they have some different coordinate: for example, if x1 != x1′. Examples First […]

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Leetcode 895: Maximum Frequency Stack

Leetcode 895: Maximum Frequency Stack

CATEGORY: HARD Problem Design a stack-like data structure to push elements to the stack and pop the most frequent element from the stack. Implement the FreqStack class: Examples First Example : Constraints: Solution Approach Solution Logic In this problem of Maximum Frequency Stack, the main task is to find the frequency of the value in the stack.

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Leetcode 31: Next Permutation

CATEGORY: MEDIUM Problem A permutation of an array of integers is an arrangement of its members into a sequence or linear order. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally, if all the permutations of the array are sorted in one container according to their lexicographical order, then

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Leetcode 6: Zigzag Conversion

Leetcode 6: Zigzag Conversion

CATEGORY: MEDIUM Problem The string “PAYPALISHIRING” is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

And then read line by line: “PAYPALISHIRING” Write the code that will take a string and make this conversion given a number

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