[LeetCode] Spiral Matrix 解题报告
2016-01-12 11:08
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Given a matrix of m[/i] x n[/i] elements (m[/i] rows, n[/i] columns), return all elements of the matrix in spiral order.
For example,
Given the following matrix:
You should return
» Solve this problem
[解题思路]
递归式剥皮。首先剥掉最外面一层,然后递归调用剥剩余部分。 需要注意的是处理row_len和col_len为1 的情况。
这题主要是实现的难度,坐标的计算比较繁琐,算法上没有难度。
Update 2014/01/05
想了一下,递归的解法看起来还是费劲,尤其是下标的计算,很繁琐。改一下,不用递归,在一个循环里面解决,提高一下可读性。
For example,
Given the following matrix:
[ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ]
You should return
[1,2,3,6,9,8,7,4,5].
» Solve this problem
[解题思路]
递归式剥皮。首先剥掉最外面一层,然后递归调用剥剩余部分。 需要注意的是处理row_len和col_len为1 的情况。
这题主要是实现的难度,坐标的计算比较繁琐,算法上没有难度。
[code]1: vector<int> spiralOrder(vector<vector<int> > &matrix) { 2: // Start typing your C/C++ solution below 3: // DO NOT write int main() function 4: vector<int> output; 5: int row_len = matrix.size(); 6: if(row_len ==0) return output; 7: int col_len = matrix[0].size(); 8: print_order(matrix, 0, row_len, 0, col_len, output); 9: return output; 10: } 11: void print_order( 12: vector<vector<int> > &matrix, 13: int row_s, 14: int row_len, 15: int col_s, 16: int col_len, 17: vector<int>& output) 18: { 19: if(row_len<=0 || col_len <=0) return; 20: if(row_len ==1) 21: { 22: for(int i =col_s; i< col_s+col_len; i++) 23: output.push_back(matrix[row_s][i]); 24: return; 25: } 26: if(col_len ==1) 27: { 28: for(int i =row_s; i<row_s + row_len; i++) 29: output.push_back(matrix[i][col_s]); 30: return; 31: } 32: for(int i =col_s; i<col_s+col_len-1; i++) //up 33: output.push_back(matrix[row_s][i]); 34: for(int i =row_s; i<row_s+row_len-1; i++) //right 35: output.push_back(matrix[i][col_s+col_len-1]); 36: for(int i =col_s; i<col_s+col_len-1; i++) //bottom 37: output.push_back(matrix[row_s+row_len-1][2*col_s+ col_len-1 -i]); 38: for(int i =row_s; i<row_s+row_len-1; i++) //left 39: output.push_back(matrix[2*row_s+row_len-1-i][col_s]); 40: print_order(matrix, row_s+1, row_len-2, col_s+1, col_len-2, output); 41: }
Update 2014/01/05
想了一下,递归的解法看起来还是费劲,尤其是下标的计算,很繁琐。改一下,不用递归,在一个循环里面解决,提高一下可读性。
1 vector<int> spiralOrder(vector<vector<int> > &matrix) { 2 vector<int> result; 3 int row = matrix.size(); 4 if(row == 0) return result; 5 int col = matrix[0].size(); 6 if(col == 0) return result; 7 8 //define the step for 4 directions 9 int x[4] = { 1, 0, -1, 0 }; 10 int y[4] = { 0, 1, 0, -1 }; 11 12 int visitedRows = 0; 13 int visitedCols = 0; 14 15 // define direction: 0 means up, 1 means down, 2 means left, 3 means up 16 int direction = 0; 17 int startx = 0, starty = 0; 18 int candidateNum = 0, moveStep = 0; 19 while (true) 20 { 21 if (x[direction] == 0) // visit y axis 22 candidateNum = row - visitedRows; 23 else // visit x axis 24 candidateNum = col - visitedCols; 25 26 if (candidateNum <= 0) 27 break; 28 result.push_back(matrix[starty][startx]); 29 moveStep++; 30 if (candidateNum == moveStep) // change direction 31 { 32 visitedRows += x[direction] == 0 ? 0 : 1; 33 visitedCols += y[direction] == 0 ? 0 : 1; 34 direction = (direction + 1) % 4; 35 moveStep = 0; 36 } 37 startx += x[direction]; 38 starty += y[direction]; 39 } 40 return result; 41 }
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