Create 1759-count-number-of-homogenous-substrings.js

Author: everthis

1759-count-number-of-homogenous-substrings.js

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+/**
+ * @param {string} s
+ * @return {number}
+ */
+const countHomogenous = function(s) {
+  const mod = 10 ** 9 + 7
+  let pre = s[0], res = 0, curL = 1
+  for(let i = 1, len = s.length; i < len; i++) {
+    if(s[i] === pre) {
+      curL++
+    } else {
+      res = (res + helper(curL)) % mod
+      pre = s[i]
+      curL = 1
+    }
+  }
+  if(curL === 1) res = (res + 1) % mod
+  else res = (res + helper(curL)) % mod
+  return res
+
+  function helper(num) {
+     return (num * (num + 1)) / 2
+  }
+};
+