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Author: Ysc

Java/Array/7-lucky numbers in a matrix.md

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+Easy Leetcode 1380  
+1517474043
+tags: Array
+
+[lucky numvers in a matrix](https://leetcode.com/problems/lucky-numbers-in-a-matrix/)
+
+方法1:
+命令式解题。先找最大值，再找最小值。我的解法
+方法2：
+通过数学证明，这样的数字之恶能存在一个
+
+
+
+    /*
+    方法1
+    */
+    class Solution {
+        public List<Integer> luckyNumbers (int[][] matrix) {
+            int m = matrix.length;
+            List<Integer> result = new LinkedList<>();
+            for (int i = 0; i < m; i++) {
+                int[] row = matrix[i];
+                int index = findMin(row);
+                boolean flag = true;
+                for (int j = 0; j < m; j++) {
+                    if(matrix[j][index]  > matrix[i][index]) {
+                        flag = false;
+                        break;
+                    }
+                }
+                if(flag) {
+                    result.add(matrix[i][index]);
+                }
+    
+            }
+            return result;
+        }
+        
+        public static int findMin(int[] x) {
+              int min = x[0];
+              int index = 0;
+              for(int i = 0; i < x.length; i++) {
+                  if(x[i] < min) {
+                      min = x[i];
+                      index = i;
+                  }
+              }
+              return index;
+        }
+    }
+    
+    
+    /*
+    方法2
+    */
+        public List<Integer> luckyNumbers (int[][] matrix) {
+            Set<Integer> minSet = new HashSet<>(), maxSet = new HashSet<>();
+            for (int[] row : matrix) {
+                int mi = row[0];
+                for (int cell : row)
+                    mi = Math.min(mi, cell);
+                minSet.add(mi);
+            }
+            for (int j = 0; j < matrix[0].length; ++j) {
+                int mx = matrix[0][j];
+                for (int i = 0; i < matrix.length; ++i)
+                    mx = Math.max(matrix[i][j], mx);
+                if (minSet.contains(mx))
+                    maxSet.add(mx);
+            }
+            return new ArrayList<>(maxSet);        
+        }
+