Create 629-k-inverse-pairs-array.js

Author: everthis

629-k-inverse-pairs-array.js

@@ -0,0 +1,19 @@
+/**
+ * @param {number} n
+ * @param {number} k
+ * @return {number}
+ */
+const kInversePairs = function(n, k) {
+  const dp = Array.from({ length: n + 1 }, () => new Array(k + 1).fill(0))
+  for (let i = 1; i < n + 1; i++) {
+    dp[i][0] = 1
+  }
+  const MOD = 1e9 + 7
+  for (let i = 1; i < n + 1; i++) {
+    for (let j = 1; j < k + 1; j++) {
+      let val = (dp[i - 1][j] - (j >= i ? dp[i - 1][j - i] : 0) + MOD) % MOD
+      dp[i][j] = (dp[i][j - 1] + val) % MOD
+    }
+  }
+  return (dp[n][k] - (dp[n][k - 1] || 0) + MOD) % MOD
+}