SetMatrixZeroes

Change-Id: Id82c30a5eb860bd4dd0493ba7ae03a1ff247bc07

Author: applewjg

SetMatrixZeroes.java

@@ -0,0 +1,60 @@
+/*
+ Author:     King, [email protected]
+ Date:       Dec 25, 2014
+ Problem:    Set Matrix Zeroes
+ Difficulty: Medium
+ Source:     https://oj.leetcode.com/problems/set-matrix-zeroes/
+ Notes:
+ Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.
+ 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?
+
+ Solution: Use first row and column as auxiliary spaces instead of newly allocating ones.
+*/
+public class Solution {
+    public void setZeroes(int[][] matrix) {
+        int m = matrix.length;
+        if(m <= 0) return;
+        int n = matrix[0].length;
+        
+        boolean row_has_zero = false;
+        boolean col_has_zero = false;
+        
+        for(int j=0; j<n;j++){
+            if(matrix[0][j]==0){
+                row_has_zero = true;
+                break;
+            }
+        }
+        for(int i=0; i<m;i++){
+            if(matrix[i][0]==0){
+                col_has_zero = true;
+                break;
+            }
+        }
+        
+        for(int i=0;i<m;i++){
+            for(int j=0;j<n;j++){
+                if(matrix[i][j]==0){
+                    matrix[0][j] =0;
+                    matrix[i][0] =0;
+                }
+            }
+        }
+        for (int i = 1; i < m; i++)
+            for (int j = 1; j < n; j++)
+                if (matrix[i][0] == 0 || matrix[0][j] == 0)
+                    matrix[i][j] = 0;
+
+        if (row_has_zero)
+            for (int i = 0; i < n; i++)
+                matrix[0][i] = 0;
+        if (col_has_zero)
+            for (int i = 0; i < m; i++)
+                matrix[i][0]=0;
+        
+    }  
+}