feat: update solutions to lc problems: No.1572,1574

* No.1572.Matrix Diagonal Sum
* No.1574.Shortest Subarray to be Removed to Make Array Sorted

Author: yanglbme

solution/1500-1599/1572.Matrix Diagonal Sum/README.md

@@ -56,6 +56,14 @@
 
 <!-- 这里可写通用的实现逻辑 -->
 
+**方法一：逐行遍历**
+
+我们可以遍历矩阵的每一行 $row[i]$，对于每一行，我们可以计算出两个对角线上的元素，即 $row[i][i]$ 和 $row[i][n - i - 1]$，其中 $n$ 是矩阵的行数。如果 $i = n - i - 1$，则说明当前行的对角线上只有一个元素，否则有两个元素。我们将其加到答案中即可。
+
+遍历完所有行后，即可得到答案。
+
+时间复杂度 $O(n)$，空间复杂度 $O(1)$。其中 $n$ 是矩阵的行数。
+
 <!-- tabs:start -->
 
 ### **Python3**
@@ -65,11 +73,12 @@
 ```python
 class Solution:
     def diagonalSum(self, mat: List[List[int]]) -> int:
+        ans = 0
         n = len(mat)
-        res = 0
-        for i in range(n):
-            res += mat[i][i] + (0 if n - i - 1 == i else mat[i][n - i - 1])
-        return res
+        for i, row in enumerate(mat):
+            j = n - i - 1
+            ans += row[i] + (0 if j == i else row[j])
+        return ans
 ```
 
 ### **Java**
@@ -79,12 +88,13 @@ class Solution:
 ```java
 class Solution {
     public int diagonalSum(int[][] mat) {
+        int ans = 0;
         int n = mat.length;
-        int res = 0;
         for (int i = 0; i < n; ++i) {
-            res += mat[i][i] + (n - i - 1 == i ? 0 : mat[i][n - i - 1]);
+            int j = n - i - 1;
+            ans += mat[i][i] + (i == j ? 0 : mat[i][j]);
         }
-        return res;
+        return ans;
     }
 }
 ```
@@ -95,28 +105,29 @@ class Solution {
 class Solution {
 public:
     int diagonalSum(vector<vector<int>>& mat) {
+        int ans = 0;
         int n = mat.size();
-        int res = 0;
         for (int i = 0; i < n; ++i) {
-            res += mat[i][i] + (n - i - 1 == i ? 0 : mat[i][n - i - 1]);
+            int j = n - i - 1;
+            ans += mat[i][i] + (i == j ? 0 : mat[i][j]);
         }
-        return res;
+        return ans;
     }
 };
 ```
 
 ### **Go**
 
 ```go
-func diagonalSum(mat [][]int) int {
-	n, res := len(mat), 0
-	for i := 0; i < n; i++ {
-		res += mat[i][i]
-		if n-i-1 != i {
-			res += mat[i][n-i-1]
+func diagonalSum(mat [][]int) (ans int) {
+	n := len(mat)
+	for i, row := range mat {
+		ans += row[i]
+		if j := n - i - 1; j != i {
+			ans += row[j]
 		}
 	}
-	return res
+	return
 }
 ```
 

solution/1500-1599/1572.Matrix Diagonal Sum/README_EN.md

@@ -55,24 +55,26 @@ Notice that element mat[1][1] = 5 is counted only once.
 ```python
 class Solution:
     def diagonalSum(self, mat: List[List[int]]) -> int:
+        ans = 0
         n = len(mat)
-        res = 0
-        for i in range(n):
-            res += mat[i][i] + (0 if n - i - 1 == i else mat[i][n - i - 1])
-        return res
+        for i, row in enumerate(mat):
+            j = n - i - 1
+            ans += row[i] + (0 if j == i else row[j])
+        return ans
 ```
 
 ### **Java**
 
 ```java
 class Solution {
     public int diagonalSum(int[][] mat) {
+        int ans = 0;
         int n = mat.length;
-        int res = 0;
         for (int i = 0; i < n; ++i) {
-            res += mat[i][i] + (n - i - 1 == i ? 0 : mat[i][n - i - 1]);
+            int j = n - i - 1;
+            ans += mat[i][i] + (i == j ? 0 : mat[i][j]);
         }
-        return res;
+        return ans;
     }
 }
 ```
@@ -83,28 +85,29 @@ class Solution {
 class Solution {
 public:
     int diagonalSum(vector<vector<int>>& mat) {
+        int ans = 0;
         int n = mat.size();
-        int res = 0;
         for (int i = 0; i < n; ++i) {
-            res += mat[i][i] + (n - i - 1 == i ? 0 : mat[i][n - i - 1]);
+            int j = n - i - 1;
+            ans += mat[i][i] + (i == j ? 0 : mat[i][j]);
         }
-        return res;
+        return ans;
     }
 };
 ```
 
 ### **Go**
 
 ```go
-func diagonalSum(mat [][]int) int {
-	n, res := len(mat), 0
-	for i := 0; i < n; i++ {
-		res += mat[i][i]
-		if n-i-1 != i {
-			res += mat[i][n-i-1]
+func diagonalSum(mat [][]int) (ans int) {
+	n := len(mat)
+	for i, row := range mat {
+		ans += row[i]
+		if j := n - i - 1; j != i {
+			ans += row[j]
 		}
 	}
-	return res
+	return
 }
 ```
 

solution/1500-1599/1572.Matrix Diagonal Sum/Solution.cpp

@@ -1,11 +1,12 @@
 class Solution {
 public:
     int diagonalSum(vector<vector<int>>& mat) {
+        int ans = 0;
         int n = mat.size();
-        int res = 0;
         for (int i = 0; i < n; ++i) {
-            res += mat[i][i] + (n - i - 1 == i ? 0 : mat[i][n - i - 1]);
+            int j = n - i - 1;
+            ans += mat[i][i] + (i == j ? 0 : mat[i][j]);
         }
-        return res;
+        return ans;
     }
 };

solution/1500-1599/1572.Matrix Diagonal Sum/Solution.go

@@ -1,10 +1,10 @@
-func diagonalSum(mat [][]int) int {
-	n, res := len(mat), 0
-	for i := 0; i < n; i++ {
-		res += mat[i][i]
-		if n-i-1 != i {
-			res += mat[i][n-i-1]
+func diagonalSum(mat [][]int) (ans int) {
+	n := len(mat)
+	for i, row := range mat {
+		ans += row[i]
+		if j := n - i - 1; j != i {
+			ans += row[j]
 		}
 	}
-	return res
+	return
 }

solution/1500-1599/1572.Matrix Diagonal Sum/Solution.java

@@ -1,10 +1,11 @@
 class Solution {
     public int diagonalSum(int[][] mat) {
+        int ans = 0;
         int n = mat.length;
-        int res = 0;
         for (int i = 0; i < n; ++i) {
-            res += mat[i][i] + (n - i - 1 == i ? 0 : mat[i][n - i - 1]);
+            int j = n - i - 1;
+            ans += mat[i][i] + (i == j ? 0 : mat[i][j]);
         }
-        return res;
+        return ans;
     }
 }

solution/1500-1599/1572.Matrix Diagonal Sum/Solution.py

@@ -1,7 +1,8 @@
 class Solution:
     def diagonalSum(self, mat: List[List[int]]) -> int:
+        ans = 0
         n = len(mat)
-        res = 0
-        for i in range(n):
-            res += mat[i][i] + (0 if n - i - 1 == i else mat[i][n - i - 1])
-        return res
+        for i, row in enumerate(mat):
+            j = n - i - 1
+            ans += row[i] + (0 if j == i else row[j])
+        return ans