#1439 - Find the Kth Smallest Sum of a Matrix With Sorted Rows

Hard • View on LeetCode • View on GitHub

Array Binary Search Matrix Heap Priority Queue

Problem Description

You are given an m x n matrix mat that has its rows sorted in non-decreasing order and an integer k.

You are allowed to choose exactly one element from each row to form an array.

Return the kth smallest array sum among all possible arrays.

Solution

/**
 * @param {number[][]} mat
 * @param {number} k
 * @return {number}
 */
var kthSmallest = function(mat, k) {
  let sums = [0];
  const rows = mat.length;

  for (let row = 0; row < rows; row++) {
    const nextSums = [];
    for (const prevSum of sums) {
      for (const num of mat[row]) {
        nextSums.push(prevSum + num);
      }
    }
    sums = nextSums.sort((a, b) => a - b).slice(0, Math.min(k, nextSums.length));
  }

  return sums[k - 1];
};