Matrix Search - Amazon Top Interview Questions
Problem Statement :
Given a two-dimensional integer matrix, where every row and column is sorted in ascending order, find the kth (0-indexed) smallest number.
Constraints
n, m ≤ 250 where n and m are the number of rows and columns in matrix
Example 1
Input
matrix = [
[1, 3, 30],
[2, 3, 31],
[5, 5, 32]
]
k = 4
Output
5
Example 2
Input
matrix = [
[1, 2, 3]
]
k = 0
Output
1
Example 3
Input
matrix = [
[1],
[2],
[3]
]
k = 2
Output
3
Solution :
Solution in C++ :
int solve(vector<vector<int>>& A, int k) {
int M = A.size();
int N = A[0].size();
int t = N * M - k;
int l = 0;
int h = 1e7;
while (l <= h) {
int m = (l + h) >> 1;
int cnt = 0;
for (auto x : A) cnt += x.end() - upper_bound(x.begin(), x.end(), m);
if (cnt < t)
h = m - 1;
else
l = m + 1;
}
return l;
}
Solution in Java :
import java.util.*;
class Solution {
public int solve(int[][] mat, int k) {
int left = mat[0][0];
int right = mat[mat.length - 1][mat[0].length - 1];
while (left < right) {
int mid = left + (right - left) / 2;
if (possible(mat, k, mid)) {
right = mid;
} else {
left = mid + 1;
}
}
return left;
}
private boolean possible(int[][] mat, int k, int ele) {
int i = 0;
int j = mat[0].length - 1;
int count = 0;
while (i < mat.length && j >= 0) {
if (mat[i][j] > ele)
j--;
else {
count += (j + 1);
i++;
}
}
return count > k;
}
}
Solution in Python :
class Solution:
def solve(self, matrix, n):
def possible(x):
# Is the number of elements y with
# y <= x greater than n?
c = len(matrix[0]) - 1
count = 0
for row in matrix:
while c >= 0 and row[c] > x:
c -= 1
count += c + 1
return count > n
lo = matrix[0][0]
hi = matrix[-1][-1]
while lo < hi:
mi = lo + hi >> 1
if not possible(mi):
lo = mi + 1
else:
hi = mi
return lo
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