0074. Search a 2D Matrix

Author: coderbean

markdown/0074. Search a 2D Matrix.md

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+### [74\. Search a 2D Matrix](https://leetcode.com/problems/search-a-2d-matrix/)
+
+Difficulty: **Medium**
+
+
+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.
+
+**Example 1:**
+
+```
+Input:
+matrix = [
+  [1,   3,  5,  7],
+  [10, 11, 16, 20],
+  [23, 30, 34, 50]
+]
+target = 3
+Output: true
+```
+
+**Example 2:**
+
+```
+Input:
+matrix = [
+  [1,   3,  5,  7],
+  [10, 11, 16, 20],
+  [23, 30, 34, 50]
+]
+target = 13
+Output: false
+```
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+class Solution {
+    public boolean searchMatrix(int[][] matrix, int target) {
+        if (matrix == null || matrix.length == 0) {
+            return false;
+        }
+        int rows = matrix.length;
+        int width = matrix[0].length;
+​
+        if (width == 0) {
+            return false;
+        }
+        int targetRowIndex = -1;
+        for (int i = 0; i < rows; i++) {
+            if (matrix[i][0] <= target && matrix[i][width - 1] >= target) {
+                targetRowIndex = i;
+                break;
+            }
+        }
+        if (targetRowIndex < 0) {
+            return false;
+        }
+        int[] targetRow = matrix[targetRowIndex];
+​
+        int left = 0;
+        int right = width;
+        int medium;
+        while (left < right) {
+            medium = (left + right) / 2;
+            if (targetRow[medium] == target) {
+                return true;
+            } else if (targetRow[medium] > target) {
+                right = medium;
+            } else {
+                left = medium + 1;
+            }
+        }
+        return false;
+    }
+}
+```
+![pic](https://gitee.com/jacobchang/PicBed/raw/master/HGYqH5.png)

src/main/java/leetcode/_74_/Main.java

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+package leetcode._74_;
+
+/**
+ * Created by zhangbo54 on 2019-03-04.
+ */
+public class Main {
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        int[][] matrix = {
+                {
+                        1, 3, 5, 7
+                },
+                {
+                        10, 11, 16, 20
+                },
+                {
+                        23, 30, 34, 50
+                }
+        };
+        System.out.println(solution.searchMatrix(matrix, 3));
+
+        int[][] matrix2 = {
+                {
+                        1, 3, 5, 7
+                },
+                {
+                        10, 11, 16, 20
+                },
+                {
+                        23, 30, 34, 50
+                }
+        };
+        System.out.println(solution.searchMatrix(matrix2, 13));
+        int[][] matrix3 = {
+                {
+                        1
+                }
+        };
+        System.out.println(solution.searchMatrix(matrix3, 0));
+
+    }
+}
+

src/main/java/leetcode/_74_/Solution.java

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+package leetcode._74_;
+
+class Solution {
+    public boolean searchMatrix(int[][] matrix, int target) {
+        if (matrix == null || matrix.length == 0) {
+            return false;
+        }
+        int rows = matrix.length;
+        int width = matrix[0].length;
+
+        if (width == 0) {
+            return false;
+        }
+        int targetRowIndex = -1;
+        for (int i = 0; i < rows; i++) {
+            if (matrix[i][0] <= target && matrix[i][width - 1] >= target) {
+                targetRowIndex = i;
+                break;
+            }
+        }
+        if (targetRowIndex < 0) {
+            return false;
+        }
+        int[] targetRow = matrix[targetRowIndex];
+
+        int left = 0;
+        int right = width;
+        int medium;
+        while (left < right) {
+            medium = (left + right) / 2;
+            if (targetRow[medium] == target) {
+                return true;
+            } else if (targetRow[medium] > target) {
+                right = medium;
+            } else {
+                left = medium + 1;
+            }
+        }
+        return false;
+    }
+}

src/main/java/leetcode/_74_/solution.md

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+### [74\. Search a 2D Matrix](https://leetcode.com/problems/search-a-2d-matrix/)
+
+Difficulty: **Medium**
+
+
+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.
+
+**Example 1:**
+
+```
+Input:
+matrix = [
+  [1,   3,  5,  7],
+  [10, 11, 16, 20],
+  [23, 30, 34, 50]
+]
+target = 3
+Output: true
+```
+
+**Example 2:**
+
+```
+Input:
+matrix = [
+  [1,   3,  5,  7],
+  [10, 11, 16, 20],
+  [23, 30, 34, 50]
+]
+target = 13
+Output: false
+```
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+class Solution {
+    public boolean searchMatrix(int[][] matrix, int target) {
+        if (matrix == null || matrix.length == 0) {
+            return false;
+        }
+        int rows = matrix.length;
+        int width = matrix[0].length;
+​
+        if (width == 0) {
+            return false;
+        }
+        int targetRowIndex = -1;
+        for (int i = 0; i < rows; i++) {
+            if (matrix[i][0] <= target && matrix[i][width - 1] >= target) {
+                targetRowIndex = i;
+                break;
+            }
+        }
+        if (targetRowIndex < 0) {
+            return false;
+        }
+        int[] targetRow = matrix[targetRowIndex];
+​
+        int left = 0;
+        int right = width;
+        int medium;
+        while (left < right) {
+            medium = (left + right) / 2;
+            if (targetRow[medium] == target) {
+                return true;
+            } else if (targetRow[medium] > target) {
+                right = medium;
+            } else {
+                left = medium + 1;
+            }
+        }
+        return false;
+    }
+}
+```
+![pic](https://gitee.com/jacobchang/PicBed/raw/master/HGYqH5.png)