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SpiralOrder54.java
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SpiralOrder54.java
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package Leetcode;
import java.util.ArrayList;
import java.util.List;
public class SpiralOrder54 {
/* Method: Traversal by layer , Time: O(M*N), Space:O(1)**/
public List<Integer> spiralOrder(int[][] matrix) {
List<Integer> res = new ArrayList<>();
if(matrix.length == 0 || matrix[0].length == 0) {
return res;
}
int left = 0;
int right = matrix[0].length - 1;
int up = 0;
int down = matrix.length - 1;
while(true) {
for(int col = left; col <= right; col ++) {
res.add(matrix[up][col]);
}
up++;
if(up>down) {
break;
}
for(int row = up; row <= down; row ++) {
res.add(matrix[row][right]);
}
right--;
if(right<left) {
break;
}
for(int col = right; col >= left; col -- ) {
res.add(matrix[down][col]);
}
down--;
if(down < up) {
break;
}
for(int row = down; row >= up; row --) {
res.add(matrix[row][left]);
}
left++;
if(left>right) {
break;
}
}
return res;
}
}