reduced string

Author: Narahari-Sundaragopalan

FE-JS-Questions/ReduceString.md

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+> Given a string return a reduced string such that , the reduced string has the characters re-arranged
+
+* in order of characters having highest frequencey
+* followed by character which appears just once in the same order as in the original string
+* and no duplicate characters
+
+```
+Input: "hello world"
+Output: "lohe wrd"
+Explaination: 'l' appears thrice, 'o' appears twice, 'h','e', ' '(space) ,'w','r','d' all appear once 
+'h','e',' ','w','r','d' should be appended in the same order as they appear in the original string  hello world
+```
+
+```js
+const reducedString = str => {
+    const charMap = new Map();
+
+    for (let char of str.split('')) {
+        charMap.has(char) ? charMap.set(char, charMap.get(char) + 1) : charMap.set(char, 1);
+    }
+
+    return (
+            [...charMap.entries()]
+            .sort((a, b) => b[1] - a[1])
+            .map(s => s[0])
+            ).join('');
+}
+```

exercises/arrays/summaryRanges.js

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+/**
+ * Given a unsorted integer array without duplicates, return the summary of its ranges.
+
+Example 1:
+
+Input:  [0,1,2,4,5,7]
+Output: ["0->2","4->5","7"]
+Explanation: 0,1,2 form a continuous range; 4,5 form a continuous range.
+Example 2:
+
+Input:  [0,2,3,4,6,8,9]
+Output: ["0","2->4","6","8->9"]
+Explanation: 2,3,4 form a continuous range; 8,9 form a continuous range.
+ */
+
+const summaryRanges = nums => {
+    if (nums.length === 0) {
+        return [];
+    }
+
+    nums.sort((a, b) => a - b);
+    const result = [];
+
+    for (let start = 0, end = 0; end < nums.length; end++) {
+        if (end + 1 < nums.length && nums[end + 1] === nums[end] + 1) {
+            continue;
+        }
+
+        if (start === end) {
+            result.push(nums[start] + '');
+        } else {
+            result.push(start + '->' + end);
+        }
+        start = end + 1;
+    }
+
+    return result;
+}