Luogu P4783 【模板】矩阵求逆

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int n, n2; // n2 = n * 2
int a[MAXn + 10][MAXn * 2 + 10];
bool EvaInv() {
    for (int i = 1; i <= n; ++i) {
        a[i][i + n] = 1;
    }
    for (int i = 1; i <= n; ++i) {
        int chose = 0;
        for (int j = i; j <= n; ++j) {
            if (a[j][i]) {
                chose = j;
                break;
            }
        }
        if (chose == 0) return 0;
        if (chose != i) {
            for (int j = 1; j <= n2; ++j) {
                swap(a[i][j], a[chose][j]);
            }
        }
        int invaii = inv(a[i][i]);
        for (int j = i; j <= n2; ++j) {
            a[i][j] = a[i][j] * invaii % MOD;
        }
        for (int j = 1; j <= n; ++j) {
            if (j == i) continue;
            int mul = a[j][i];
            for (int k = i; k <= n2; ++k) {
                a[j][k] -= a[i][k] * mul % MOD;
                redmod(a[j][k]);
            }
        }
    }
    return 1;
}