Time: 15 ms (66.48%), Space: 17.5 MB (13.19%) - LeetHub

Author: knockcat

0629-k-inverse-pairs-array/0629-k-inverse-pairs-array.cpp

@@ -0,0 +1,24 @@
+class Solution {
+public:
+    int mod = 1e9+7;
+    int kInversePairs(int n, int K) {
+        //dp[i][j] denote till i numbers how many jth inversion pair-containing permutations are there
+        vector<vector<int>> dp(n+1,vector<int>(K+1,0));
+        dp[0][0]=0;
+        for(int i=1;i<=K;i++){
+            dp[1][i]=0;
+        }
+        for(int i=1;i<=n;i++){
+            dp[i][0]=1;
+        }
+for(int i=2;i<=n;i++){
+            for(int j=1;j<=K;j++){
+                dp[i][j]=(dp[i-1][j]+dp[i][j-1])%mod;
+                if(j-i>=0){
+                    dp[i][j]=(dp[i][j]-dp[i-1][j-i]+mod)%mod;
+                }
+            }         
+        }
+        return dp[n][K];
+    }
+};