refactor 74

Author: fishercoder1534

README.md

@@ -529,7 +529,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |77|[Combinations](https://leetcode.com/problems/combinations/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_77.java)|O(n^2) ? |O(1)|Medium|Backtracking
 |76|[Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_76.java)|O(n)|O(k)|Hard|Two Pointers
 |75|[Sort Colors](https://leetcode.com/problems/sort-colors/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_75.java)|O(n)|O(1)|Medium| Two Pointers
-|74|[Search a 2D Matrix](https://leetcode.com/problems/search-a-2d-matrix/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_74.java)|O(logn)|O(1)|Medium| Binary Search
+|74|[Search a 2D Matrix](https://leetcode.com/problems/search-a-2d-matrix/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_74.java)|O(log(m*n))|O(1)|Medium| Binary Search
 |73|[Set Matrix Zeroes](https://leetcode.com/problems/set-matrix-zeroes/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_73.java)|O(mn)|O(mn)|Medium|
 |72|[Edit Distance](https://leetcode.com/problems/edit-distance/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_72.java)|O(m*n)|O(m+n)|Hard| 
 |71|[Simplify Path](https://leetcode.com/problems/simplify-path/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_71.java)|O(n)|O(n)|Medium| Stack

src/main/java/com/fishercoder/solutions/_74.java

@@ -1,7 +1,10 @@
 package com.fishercoder.solutions;
 
 /**
- * Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:
+ * 74. Search a 2D Matrix
+ *
+ * Write an efficient algorithm that searches for a value in an m x n matrix.
+ * This matrix has the following properties:
 
  Integers in each row are sorted from left to right.
  The first integer of each row is greater than the last integer of the previous row.
@@ -21,18 +24,28 @@
 public class _74 {
 
     public boolean searchMatrix(int[][] matrix, int target) {
-        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) return false;
-        int m = matrix.length, n = matrix[0].length;
-        if (target < matrix[0][0] || target > matrix[m-1][n-1]) return false;
-        //just treat it as a sorted list
+        if (matrix == null || matrix.length == 0
+                || matrix[0].length == 0
+                || matrix[0][0] > target
+                || matrix[matrix.length-1][matrix[0].length-1] < target) {
+            return false;
+        }
+        int m = matrix.length;
+        int n = matrix[0].length;
         int left = 0;
-        int right = m*n - 1;
-        while (left != right) {
-            int mid = (left + right - 1) >> 1;
-            if (matrix[mid/n][mid%n] < target) left = mid + 1;
-            else right = mid;
+        int right = m * n - 1 ;
+        while (left <= right) {
+            int mid = left + (right-left)/2;
+            int row = mid/n;
+            int col = mid%n;
+            if (matrix[row][col] == target) {
+                return true;
+            } else if (matrix[row][col] > target) {
+                right = mid-1;
+            } else {
+                left = mid+1;
+            }
         }
-        return matrix[right/n][right%n] == target;
+        return false;
     }
-
 }