Sparse Matrix Multiplication
https://leetcode.com/problems/sparse-matrix-multiplication/description/
http://www.jiuzhang.com/solutions/sparse-matrix-multiplication/
public class Solution {
/**
* @param A a sparse matrix
* @param B a sparse matrix
* @return the result of A * B
*/
public int[][] multiply(int[][] A, int[][] B) {
// Write your code here
int n = A.length;
int m = B[0].length;
int t = A[0].length;
int[][] C = new int[n][m];
for (int i = 0; i < n; i++) {
for (int k = 0; k < t; k++) {
if (A[i][k] == 0) {
continue;
}
for (int j = 0; j < m; j++) {
C[i][j] += A[i][k] * B[k][j];
}
}
}
return C;
}
}
public class Solution {
/**
* @param A a sparse matrix
* @param B a sparse matrix
* @return the result of A * B
*/
public int[][] multiply(int[][] A, int[][] B) {
// Write your code here
int n = A.length;
int m = B[0].length;
int t = A[0].length;
int[][] C = new int[n][m];
List<List<Integer>> val = new ArrayList<>();
List<List<Integer>> col = new ArrayList<>();
for (int i = 0; i < t; i++) {
val.add(new ArrayList<>());
col.add(new ArrayList<>());
for (int j = 0; j < m; j++) {
if (B[i][j] != 0) {
col.get(i).add(j);
val.get(i).add(B[i][j]);
}
}
}
for (int i = 0; i < n; i++) {
for (int k = 0; k < t; k++) {
if (A[i][k] != 0) {
for (int p = 0; p < col.get(k).size(); p++) {
int j = col.get(k).get(p);
int v = val.get(k).get(p);
C[i][j] += A[i][k] * v;
}
}
}
}
return C;
}
}