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Merge pull request #901 from kvedala/fixes/lgtm
bugs: fix warnings in matrix_exponentiation
2 parents 3fc8532 + ef5f330 commit 8476290

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others/matrix_exponentiation.cpp

Lines changed: 25 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -39,18 +39,15 @@ using std::vector;
3939
#define pb push_back
4040
#define MOD 1000000007
4141

42-
/** returns absolute value */
43-
inline ll ab(ll x) { return x > 0LL ? x : -x; }
44-
45-
/** global variable k
42+
/** global variable mat_size
4643
* @todo @stepfencurryxiao add documetnation
4744
*/
48-
ll k;
45+
ll mat_size;
4946

50-
/** global vector variables
47+
/** global vector variables used in the ::ans function.
5148
* @todo @stepfencurryxiao add documetnation
5249
*/
53-
vector<ll> a, b, c;
50+
vector<ll> fib_b, fib_c;
5451

5552
/** To multiply 2 matrices
5653
* \param [in] A matrix 1 of size (m\f$\times\f$n)
@@ -59,10 +56,10 @@ vector<ll> a, b, c;
5956
*/
6057
vector<vector<ll>> multiply(const vector<vector<ll>> &A,
6158
const vector<vector<ll>> &B) {
62-
vector<vector<ll>> C(k + 1, vector<ll>(k + 1));
63-
for (ll i = 1; i <= k; i++) {
64-
for (ll j = 1; j <= k; j++) {
65-
for (ll z = 1; z <= k; z++) {
59+
vector<vector<ll>> C(mat_size + 1, vector<ll>(mat_size + 1));
60+
for (ll i = 1; i <= mat_size; i++) {
61+
for (ll j = 1; j <= mat_size; j++) {
62+
for (ll z = 1; z <= mat_size; z++) {
6663
C[i][j] = (C[i][j] + (A[i][z] * B[z][j]) % MOD) % MOD;
6764
}
6865
}
@@ -94,32 +91,32 @@ vector<vector<ll>> power(const vector<vector<ll>> &A, ll p) {
9491
ll ans(ll n) {
9592
if (n == 0)
9693
return 0;
97-
if (n <= k)
98-
return b[n - 1];
94+
if (n <= mat_size)
95+
return fib_b[n - 1];
9996
// F1
100-
vector<ll> F1(k + 1);
101-
for (ll i = 1; i <= k; i++) F1[i] = b[i - 1];
97+
vector<ll> F1(mat_size + 1);
98+
for (ll i = 1; i <= mat_size; i++) F1[i] = fib_b[i - 1];
10299

103100
// Transpose matrix
104-
vector<vector<ll>> T(k + 1, vector<ll>(k + 1));
105-
for (ll i = 1; i <= k; i++) {
106-
for (ll j = 1; j <= k; j++) {
107-
if (i < k) {
101+
vector<vector<ll>> T(mat_size + 1, vector<ll>(mat_size + 1));
102+
for (ll i = 1; i <= mat_size; i++) {
103+
for (ll j = 1; j <= mat_size; j++) {
104+
if (i < mat_size) {
108105
if (j == i + 1)
109106
T[i][j] = 1;
110107
else
111108
T[i][j] = 0;
112109
continue;
113110
}
114-
T[i][j] = c[k - j];
111+
T[i][j] = fib_c[mat_size - j];
115112
}
116113
}
117114
// T^n-1
118115
T = power(T, n - 1);
119116

120117
// T*F1
121118
ll res = 0;
122-
for (ll i = 1; i <= k; i++) {
119+
for (ll i = 1; i <= mat_size; i++) {
123120
res = (res + (T[1][i] * F1[i]) % MOD) % MOD;
124121
}
125122
return res;
@@ -133,19 +130,19 @@ int main() {
133130
cin >> t;
134131
ll i, j, x;
135132
while (t--) {
136-
cin >> k;
137-
for (i = 0; i < k; i++) {
133+
cin >> mat_size;
134+
for (i = 0; i < mat_size; i++) {
138135
cin >> x;
139-
b.pb(x);
136+
fib_b.pb(x);
140137
}
141-
for (i = 0; i < k; i++) {
138+
for (i = 0; i < mat_size; i++) {
142139
cin >> x;
143-
c.pb(x);
140+
fib_c.pb(x);
144141
}
145142
cin >> x;
146143
cout << ans(x) << endl;
147-
b.clear();
148-
c.clear();
144+
fib_b.clear();
145+
fib_c.clear();
149146
}
150147
return 0;
151148
}

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