Solve the "Search in a 2D sorted array" problem

README.md

@@ -170,7 +170,7 @@ Searching
 
 | Problem                                                                  | Test         | Implemented |
 |--------------------------------------------------------------------------|:------------:|:-----------:|
-| [Search in a 2D sorted array][200]                                       | [tests][201] |             |
+| [Search in a 2D sorted array][200]                                       | [tests][201] |      ✓      |
 | [Find the min and max simultaneously][202]                               | [tests][203] |             |
 | [Find the *k*th largest element][204]                                    | [tests][205] |             |
 | [Compute the optimum mailbox placement][206]                             | [tests][207] |             |
@@ -603,8 +603,8 @@ Honors Class
 [197]: in_progress.md
 [198]: in_progress.md
 [199]: in_progress.md
-[200]: in_progress.md
-[201]: in_progress.md
+[200]: search/matrix.go
+[201]: search/matrix_test.go
 [202]: in_progress.md
 [203]: in_progress.md
 [204]: in_progress.md

search/matrix.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2015, Peter Mrekaj. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE.txt file.
+
+package search
+
+// Matrix returns true if m contains x, otherwise returns false.
+// The time complexity is O(m+n) where m is number of row and n is
+// number of columns in matrix. The O(1) additional space is needed.
+func Matrix(m [][]int, x int) bool {
+	r, c := 0, len(m)-1
+	for r < len(m) && c >= 0 {
+		switch e := m[r][c]; {
+		case e == x:
+			return true
+		case e > x:
+			c--
+		case e < x:
+			r++
+		}
+	}
+	return false
+}

search/matrix_test.go

@@ -0,0 +1,48 @@
+// Copyright (c) 2015, Peter Mrekaj. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE.txt file.
+
+package search
+
+import (
+	"math/rand"
+	"sort"
+	"testing"
+)
+
+func TestMatrix(t *testing.T) {
+	for _, test := range []struct {
+		m    [][]int
+		x    int
+		want bool
+	}{
+		{[][]int{[]int{0, 1}, []int{1, 2}}, 2, true},
+		{[][]int{[]int{0, 1}, []int{1, 2}}, -1, false},
+		{[][]int{[]int{0, 1, 2}, []int{1, 2, 3}, []int{2, 3, 4}}, 2, true},
+		{[][]int{[]int{0, 1, 2}, []int{1, 2, 3}, []int{2, 3, 4}}, -1, false},
+	} {
+		if got := Matrix(test.m, test.x); got != test.want {
+			t.Errorf("Matrix(%v, %d) = %t; want %t", test.m, test.x, got, test.want)
+		}
+	}
+}
+
+func benchMatrix(b *testing.B, size int) {
+	b.StopTimer()
+	n := size * size
+	data := rand.Perm(n)
+	sort.Ints(data)
+	x := data[n/2]
+	var m [][]int
+	for i := 1; i <= size; i++ {
+		m = append(m, data[(i-1)*size:i*size])
+	}
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Matrix(m, x)
+	}
+}
+
+func BenchmarkMatrix1e1(b *testing.B) { benchMatrix(b, 1e1) }
+func BenchmarkMatrix1e2(b *testing.B) { benchMatrix(b, 1e2) }
+func BenchmarkMatrix1e3(b *testing.B) { benchMatrix(b, 1e3) }