feat: solve No.1582

Author: BaffinLee

1501-1600/1582. Special Positions in a Binary Matrix.md

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+# 1582. Special Positions in a Binary Matrix
+
+- Difficulty: Easy.
+- Related Topics: Array, Matrix.
+- Similar Questions: Difference Between Ones and Zeros in Row and Column.
+
+## Problem
+
+Given an `m x n` binary matrix `mat`, return **the number of special positions in **`mat`**.**
+
+A position `(i, j)` is called **special** if `mat[i][j] == 1` and all other elements in row `i` and column `j` are `0` (rows and columns are **0-indexed**).
+
+ 
+Example 1:
+
+![](https://assets.leetcode.com/uploads/2021/12/23/special1.jpg)
+
+```
+Input: mat = [[1,0,0],[0,0,1],[1,0,0]]
+Output: 1
+Explanation: (1, 2) is a special position because mat[1][2] == 1 and all other elements in row 1 and column 2 are 0.
+```
+
+Example 2:
+
+![](https://assets.leetcode.com/uploads/2021/12/24/special-grid.jpg)
+
+```
+Input: mat = [[1,0,0],[0,1,0],[0,0,1]]
+Output: 3
+Explanation: (0, 0), (1, 1) and (2, 2) are special positions.
+```
+
+ 
+**Constraints:**
+
+
+	
+- `m == mat.length`
+	
+- `n == mat[i].length`
+	
+- `1 <= m, n <= 100`
+	
+- `mat[i][j]` is either `0` or `1`.
+
+
+
+## Solution
+
+```javascript
+/**
+ * @param {number[][]} mat
+ * @return {number}
+ */
+var numSpecial = function(mat) {
+    var res = 0;
+    for (var i = 0; i < mat.length; i++) {
+        var specialCol = -1;
+        var hasOnlyOne = false;
+        for (var j = 0; j < mat[i].length; j++) {
+            if (mat[i][j] === 1) {
+                if (specialCol === -1) {
+                    specialCol = j;
+                    hasOnlyOne = true;
+                } else {
+                    hasOnlyOne = false;
+                }
+            }
+        }
+        if (!hasOnlyOne) continue;
+        var isValid = true;
+        for (var k = 0; k < mat.length; k++) {
+            if (mat[k][specialCol] === 1 && k !== i) {
+                isValid = false;
+                break;
+            }
+        }
+        if (isValid) res += 1;
+    }
+    return res;
+};
+```
+
+**Explain:**
+
+nope.
+
+**Complexity:**
+
+* Time complexity : O(n * m).
+* Space complexity : O(1).