Update 903-valid-permutations-for-di-sequence.js

Author: everthis

903-valid-permutations-for-di-sequence.js

@@ -1,3 +1,44 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+const numPermsDISequence = function(s) {
+  const mod = 1e9 + 7
+  const n = s.length
+  const dp = Array.from({ length: n + 1 }, () => Array(n + 1).fill(0))
+  s = '#' + s
+  dp[0][0] = 1
+  for(let i = 1; i <= n; i++) {
+    const ch = s[i]
+    for(let j = 0; j <= i; j++) {
+      if(ch === 'I') {
+        for(let k = 0; k < j; k++) {
+          dp[i][j] += dp[i - 1][k]
+          dp[i][j] %= mod
+        }
+      } else {
+        for(let k = j; k < i; k++) {
+          dp[i][j] += dp[i - 1][k]
+          dp[i][j] %= mod
+        }
+      }
+    }
+  }
+  
+  
+  let res = 0
+  
+  for(let i = 0; i <= n; i++) {
+    res = (res + dp[n][i]) % mod
+  }
+  
+  return res
+};
+
+
+// another
+
+
 /**
  * @param {string} s
  * @return {number}