Update 0074-search-a-2d-matrix.kt

Author: a93a

kotlin/0074-search-a-2d-matrix.kt

@@ -1,7 +1,5 @@
-package kotlin
-
+// binary search on rows to find row, then binary search on actual row O(log(m*n))
 class Solution {
-
     // TC: O(log m + log n)
     fun searchMatrix(matrix: Array<IntArray>, target: Int): Boolean {
         var row = matrix.size
@@ -39,3 +37,45 @@ class Solution {
         return false
     }
 }
+
+//binary search on whole matrix (search the matrix as an sorted array) O(log(m*n))
+class Solution {
+    fun searchMatrix(mt: Array<IntArray>, t: Int): Boolean {
+        val rows = mt.size
+        val cols = mt[0].size
+
+        var l = 0
+        var r = rows * cols - 1
+        while (l != r) {
+            val m = (l + r) / 2
+            if (mt[m / cols][m % cols] < t)
+                l = m + 1
+            else
+                r = m
+        }
+
+        return mt[r / cols][r % cols] == t
+    }
+}
+
+//treat the matrix as an BST, root at mt[0][-1] O(m + n)
+class Solution {
+    fun searchMatrix(mt: Array<IntArray>, t: Int): Boolean {
+        val rows = mt.size
+        val cols = mt[0].size
+
+        var row = 0
+        var col = cols - 1
+        while (row < rows && col >= 0) {
+            val cur = mt[row][col]
+            if (cur > t)
+                col--
+            else if (cur < t)
+                row++
+            else
+                return true
+        }
+
+        return false
+    }
+}