Update 942-di-string-match.js

Author: everthis

942-di-string-match.js

@@ -22,6 +22,18 @@ const diStringMatch = function(S) {
 
 // another
 
+/*
+
+it is greedy and one pass !!
+so every time when we meet an I, we need to keep in mind that we may meet another I later,
+so the safest way is use the smallest number available. same idea when we meet D, 
+so in order to keep us safe, we always take largest one available, until we traverse the whole string.
+And since the available numbers are sorted(from 0 to S.length()), 
+so we can set two pointers one starts from the head(smallest number), 
+another from the ends(largest number), then we begin to fill the res array.
+
+*/
+
 /**
  * @param {string} s
  * @return {number[]}