451. Sort Characters By Frequency

Given a string, sort it in decreasing order based on the frequency of characters.

Example 1:

```Input:
"tree"

Output:
"eert"

Explanation:
'e' appears twice while 'r' and 't' both appear once.
So 'e' must appear before both 'r' and 't'. Therefore "eetr" is also a valid answer.
```

Example 2:

```Input:
"cccaaa"

Output:
"cccaaa"

Explanation:
Both 'c' and 'a' appear three times, so "aaaccc" is also a valid answer.
Note that "cacaca" is incorrect, as the same characters must be together.
```

Example 3:

```Input:
"Aabb"

Output:
"bbAa"

Explanation:
"bbaA" is also a valid answer, but "Aabb" is incorrect.
Note that 'A' and 'a' are treated as two different characters.

```
```class Solution {

/**
* @param String \$s
* @return String
*/
function frequencySort(\$s) {
\$c = [];
for(\$i = 0 ; \$i < strlen(\$s); \$i++){
\$char = \$s[\$i];
\$c[\$char] ++;
}

arsort(\$c);
\$result = "";
foreach(\$c as \$k => \$v){
while(\$v > 0){
\$result .= \$k;
\$v --;
}
}
return \$result;
}
}```

well, PHP is actually pretty good at this.

Doing same thing in Java is quite annoying (typing speed matters)

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