Find kth Smallest Element in a Sorted Matrix?

Short answer: int KthSmallest(int[][] matrix, int k) { int n = matrix.Length; int low = matrix[0][0], high = matrix[n - 1][n - 1]; while (low < high) { Follow on: int mid = low + (high - low) / 2; int count = 0, j = n - 1; for (int i = 0; i < n; i++) { while (j >= 0 && matrix[i][j] > mid) j--; count += (j + 1); } if (count < k) low = mid + 1; else high = mid; } return low; } Explanation: Binary search on values, count how many…

Explain a bit more

elements ≤ mid using matrix’s sorted rows/cols.

Example code

int KthSmallest(int[][] matrix, int k)
{
int n = matrix.Length;
int low = matrix[0][0], high = matrix[n - 1][n - 1]; while (low < high) { Follow on: int mid = low + (high - low) / 2;
int count = 0, j = n - 1;
for (int i = 0; i < n; i++)
{ while (j >= 0 && matrix[i][j] > mid) j--; count += (j + 1);
}
if (count < k)
low = mid + 1; else high = mid;
}
return low;
} Explanation: Binary search on values, count how many elements ≤ mid using matrix’s sorted rows/cols.

Real-world example (ShopNest)

In coding rounds, state complexity aloud, write a clear ShopNest-flavored example (orders, carts), then handle edge cases (empty list, null, overflow).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.