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export default function kthSmallest(matrix: number[][], k: number): number {    const n = matrix.length;    let left = matrix[0][0];    let right = matrix[n - 1][n - 1];    while (left < right) {        const mid = left + ((right - left) >> 1);        if (check(matrix, mid, k, n)) {            right = mid;        } else {            left = mid + 1;        }    }    return left;}
function check(matrix: number[][], mid: number, k: number, n: number) {    let i = n - 1;    let j = 0;    let num = 0;    while (i >= 0 && j < n) {        if (matrix[i][j] <= mid) {            num += i + 1;            j++;        } else {            i--;        }    }    return num >= k;}