Update 1439.Find-the-Kth-Smallest-Sum-of-a-Matrix-With-Sorted-Rows_v3…

….cpp
kushal-iitb · Jun 18, 2021 · 15f64ac · 15f64ac
1 parent 28faa74
commit 15f64ac
Showing 1 changed file with 24 additions and 20 deletions.
diff --git a/...atrix-With-Sorted-Rows/1439.Find-the-Kth-Smallest-Sum-of-a-Matrix-With-Sorted-Rows_v3.cpp b/...atrix-With-Sorted-Rows/1439.Find-the-Kth-Smallest-Sum-of-a-Matrix-With-Sorted-Rows_v3.cpp
@@ -1,21 +1,21 @@
-typedef pair<int,vector<int>> PIV;
-class Solution {    
+class Solution {
 public:
     int kthSmallest(vector<vector<int>>& mat, int k) 
     {
         int left = 0, right = INT_MAX;
         while (left < right)
         {
-            int target = left + (right-left)/2;
-            if (checkOK(mat, target, k))
+            int target = left+(right-left)/2;
+            if (checkOK(mat, target, k))  // If the # of arrays whose sum <= target is at least k
                 right = target;
             else
-                left = target + 1;
+                left = target+1;
         }
-        return left;
-    }        
-
-    // If the # of arrays whose sum <= target is at least k
+        return left;        
+    }
+
+    // Check if the # of arrays whose sum <= target is at least k
+    // o(K)
     bool checkOK(vector<vector<int>>& mat, int target, int k)
     {
         int m = mat.size();
@@ -24,29 +24,33 @@ class Solution {
         int sum = 0;
         for (int i=0; i<m; i++)
             sum += mat[i][0];
+        int count = 1;
+
         if (sum > target) return false;
 
-        int count = 1;
-        dfs(mat, 0, sum, target, count, k);
+        dfs(mat, 0, sum, count, target, k);
 
-        return (count >= k);
+        return count>=k;        
     }
-
-    void dfs(vector<vector<int>>& mat, int row, int sum, int target, int& count, int k)
+    
+    void dfs(vector<vector<int>>& mat, int row, int sum, int& count, int target, int k)
     {
         int m = mat.size();
         int n = mat[0].size();
-
+        
         if (count >= k) return;
-        if (row == m) return;
-
-        for (int j = 0; j<n; j++)
+        if (row==m) return;
+        
+        for (int j=0; j<n; j++)
         {
             if (sum + mat[row][j] - mat[row][0] <= target)
             {
                 if (j>0) count++;
-                dfs(mat, row+1, sum + mat[row][j] - mat[row][0], target, count, k);
+                dfs(mat, row+1, sum + mat[row][j] - mat[row][0], count, target, k);
             }
+            else
+                break;
         }
-    }
+    }    
 };
+