Add cpp code to sort a matrix diagonally

Author: samkit96

leetcode/cpp/sort/1329.cpp

@@ -0,0 +1,54 @@
+// Problem: https://leetcode.com/problems/sort-the-matrix-diagonally/
+
+class Solution {
+public:
+
+    // HINT: Difference of j and i is constant across a diagonal.
+    vector<vector<int>> diagonalSort(vector<vector<int>>& mat) {
+        
+        int n = mat.size();
+        if (n <=1) return mat;
+        int m = mat[0].size();
+        
+        map <int, vector<int>> mpp;
+        map <int, int> mpp2;
+        
+        for (int i=0 ; i<n ; i++) {
+            for(int j=0 ; j<m ; j++) {
+                
+                if(mpp.find(j-i)!=mpp.end()) {
+                    
+                    vector<int> v = mpp[j-i];
+                    v.push_back(mat[i][j]);
+                    mpp[j-i] = v;
+                } else {
+                    
+                    vector<int> v;
+                    v.push_back(mat[i][j]);
+                    mpp[j-i] = v;
+                }
+                
+            }
+        }
+        
+        for (auto it: mpp) {
+            
+            vector<int> v = it.second;
+            sort(v.begin(), v.end());
+            mpp[it.first] = v;
+            mpp2[it.first] = 0;
+        }
+        
+        for (int i=0 ; i<n ; i++) {
+            for(int j=0 ; j<m ; j++) {
+                
+                int idx = mpp2[j-i];
+                vector<int>v = mpp[j-i];
+                mat[i][j] = v[idx];
+                mpp2[j-i] = idx+1;
+            }
+        }
+        
+        return mat;
+    }
+};