[LEET-74] add 74

Author: fishercoder1534

leetcode-algorithms/README.md

@@ -299,6 +299,7 @@
 |78|[Subsets](https://leetcode.com/problems/subsets/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/Subsets.java)|O(n^2) ? |O(1)|Medium|Backtracking
 |76|[Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/MinimumWindowSubstring.java)|O(n)|O(k)|Hard|Two Pointers
 |75|[Sort Colors](https://leetcode.com/problems/sort-colors/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SortColors.java)|O(n)|O(1)|Medium| Two Pointers
+|74|[Search a 2D Matrix](https://leetcode.com/problems/search-a-2d-matrix/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/Searcha2DMatrix.java)|O(logn)|O(1)|Medium| Binary Search
 |73|[Set Matrix Zeroes](https://leetcode.com/problems/set-matrix-zeroes/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SetMatrixZeroes.java)|O(mn)|O(mn)|Medium|
 |72|[Edit Distance](https://leetcode.com/problems/edit-distance/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/EditDistance.java)|O(m*n)|O(m+n)|Hard| 
 |71|[Simplify Path](https://leetcode.com/problems/simplify-path/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SimplifyPath.java)|O(n)|O(n)|Medium| Stack

leetcode-algorithms/src/main/java/com/stevesun/solutions/Searcha2DMatrix.java

@@ -0,0 +1,38 @@
+package com.stevesun.solutions;
+
+/**
+ * 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.
+ For example,
+
+ Consider the following matrix:
+
+ [
+ [1,   3,  5,  7],
+ [10, 11, 16, 20],
+ [23, 30, 34, 50]
+ ]
+
+ Given target = 3, return true.
+
+ */
+public class Searcha2DMatrix {
+
+    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
+        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;
+        }
+        return matrix[right/n][right%n] == target;
+    }
+
+}

leetcode-algorithms/src/test/java/com/stevesun/Searcha2DMatrixTest.java

@@ -0,0 +1,38 @@
+package com.stevesun;
+
+import com.stevesun.solutions.Searcha2DMatrix;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.Assert.assertEquals;
+
+public class Searcha2DMatrixTest {
+    private static Searcha2DMatrix test;
+    private static boolean actual;
+    private static boolean expected;
+    private static int target;
+    private static int[][] matrix;
+
+    @BeforeClass
+    public static void setup(){
+        test = new Searcha2DMatrix();
+    }
+
+    @Before
+    public void setupForEachTest(){
+    }
+
+    @Test
+    public void test1(){
+        target = 3;
+        matrix = new int[][]{
+                {1, 3, 5, 7},
+                {10, 11, 16, 20},
+                {23, 30, 34, 50},
+        };
+        expected = true;
+        actual = test.searchMatrix(matrix, target);
+        assertEquals(expected, actual);
+    }
+}