Create 1638-count-substrings-that-differ-by-one-character.js

Author: everthis

1638-count-substrings-that-differ-by-one-character.js

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+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {number}
+ */
+const countSubstrings = function (s, t) {
+  const m = s.length
+  const n = t.length
+  const matrix = (m, n, v) => Array.from({ length: m }, () => Array(n).fill(v))
+  // number of exact same substrings ending at s[i] and t[j].
+  const same = matrix(m + 1, n + 1, 0)
+  // number of substrings having 1 different character ending at s[i] and t[j].
+  const one = matrix(m + 1, n + 1, 0)
+  let result = 0
+  for (let i = 1; i <= m; ++i) {
+    for (let j = 1; j <= n; ++j) {
+      if (s[i - 1] == t[j - 1]) {
+        same[i][j] = same[i - 1][j - 1] + 1
+        one[i][j] = one[i - 1][j - 1]
+      } else {
+        one[i][j] = same[i - 1][j - 1] + 1
+      }
+      result += one[i][j]
+    }
+  }
+  return result
+}