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algorithm/PuzzleCoding/src/SetMatrixZero.java at master · wodgithub/algorithm · GitHub
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PuzzleCoding
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src
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SetMatrixZero.java
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algorithm
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PuzzleCoding
/
src
/
SetMatrixZero.java
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import
java
.
util
.
Arrays
;
/**
* Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.
* <p/>
* Follow up:
* Did you use extra space?
* A straight forward solution using O(mn) space is probably a bad idea.
* A simple improvement uses O(m + n) space, but still not the best solution.
* Could you devise a constant space solution?
*/
public
class
SetMatrixZero
{
public
static
void
main
(
String
[]
args
) {
int
[][]
matrix
=
new
int
[][]{
{
1
,
2
,
3
,
5
},
{
2
,
4
,
0
,
1
},
{
2
,
4
,
2
,
1
},
{
0
,
4
,
2
,
1
},
};
System
.
out
.
println
(
Arrays
.
deepToString
(
matrix
));
setMatrixZero
(
matrix
);
System
.
out
.
println
(
Arrays
.
deepToString
(
matrix
));
matrix
=
new
int
[][]{
{
1
,
2
,
3
,
5
},
{
2
,
4
,
0
,
1
},
{
2
,
4
,
2
,
1
},
{
0
,
4
,
2
,
1
},
};
setZeros
(
matrix
);
System
.
out
.
println
(
Arrays
.
deepToString
(
matrix
));
}
// do it in place
// use first row/col to record zero flag
public
static
void
setMatrixZero
(
int
[][]
m
) {
if
(
m
.
length
<=
0
)
return
;
int
row
=
m
.
length
;
int
col
=
m
[
0
].
length
;
boolean
firstRowZero
=
false
;
boolean
firstColZero
=
false
;
for
(
int
j
=
0
;
j
<
col
;
j
++) {
if
(
m
[
0
][
j
] ==
0
) {
firstRowZero
=
true
;
break
;
}
}
for
(
int
i
=
0
;
i
<
row
;
i
++) {
if
(
m
[
i
][
0
] ==
0
) {
firstColZero
=
true
;
break
;
}
}
for
(
int
i
=
1
;
i
<
row
;
i
++) {
for
(
int
j
=
1
;
j
<
col
;
j
++) {
if
(
m
[
i
][
j
] ==
0
) {
// set zero flag on the first row/col
m
[
0
][
j
] =
0
;
m
[
i
][
0
] =
0
;
}
}
}
// set zero based on zero flag
for
(
int
i
=
1
;
i
<
row
;
i
++) {
for
(
int
j
=
1
;
j
<
col
;
j
++) {
if
(
m
[
0
][
j
] ==
0
||
m
[
i
][
0
] ==
0
) {
m
[
i
][
j
] =
0
;
}
}
}
if
(
firstRowZero
) {
for
(
int
j
=
0
;
j
<
col
;
j
++) {
m
[
0
][
j
] =
0
;
}
}
if
(
firstColZero
) {
for
(
int
i
=
0
;
i
<
col
;
i
++) {
m
[
i
][
0
] =
0
;
}
}
return
;
}
// need extra space O(m+n)
public
static
void
setZeros
(
int
[][]
matrix
) {
boolean
[]
row
=
new
boolean
[
matrix
.
length
];
boolean
[]
column
=
new
boolean
[
matrix
[
0
].
length
];
// Store the row and column index with value 0
for
(
int
i
=
0
;
i
<
matrix
.
length
;
i
++) {
for
(
int
j
=
0
;
j
<
matrix
[
0
].
length
;
j
++) {
if
(
matrix
[
i
][
j
] ==
0
) {
row
[
i
] =
true
;
column
[
j
] =
true
;
}
}
}
// Set arr[i][j] to 0 if either row i or column j has a 0
for
(
int
i
=
0
;
i
<
matrix
.
length
;
i
++) {
for
(
int
j
=
0
;
j
<
matrix
[
0
].
length
;
j
++) {
if
(
row
[
i
] ||
column
[
j
]) {
matrix
[
i
][
j
] =
0
;
}
}
}
}
}
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