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export default class NumMatrix {    #m: number;    #n: number;    #tree: number[][];    #nums: number[][];    constructor(matrix: number[][]) {        const m = matrix.length;        const n = matrix[0].length;        this.#m = m;        this.#n = n;        this.#tree = new Array(m + 1).fill(0).map(() => Array(n + 1).fill(0));        this.#nums = new Array(m).fill(0).map(() => Array(n).fill(0));
        matrix.forEach((a, i) => a.forEach((v, j) => this.update(i, j, v)));    }
    update(row: number, col: number, val: number) {        const delta = val - this.#nums[row][col];        this.#nums[row][col] = val;        for (let i = row + 1; i <= this.#m; i += lowbit(i)) {            for (let j = col + 1; j <= this.#n; j += lowbit(j)) {                this.#tree[i][j] += delta;            }        }    }    sumRegion(row1: number, col1: number, row2: number, col2: number): number {        return (            this.#sum(row2 + 1, col2 + 1) +            this.#sum(row1, col1) -            this.#sum(row1, col2 + 1) -            this.#sum(row2 + 1, col1)        );    }    #sum(row: number, col: number) {        let sum = 0;        for (let i = row; i > 0; i -= lowbit(i)) {            for (let j = col; j > 0; j -= lowbit(j)) {                sum += this.#tree[i][j];            }        }        return sum;    }}export function lowbit(a: number) {    return a & -a;}