runlength encoding using the input container as the output

string_compression/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "string_compression"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

string_compression/src/main.rs

@@ -0,0 +1,70 @@
+fn main() {
+    let mut a = ['a', 'a', 'b', 'b', 'c', 'c', 'c'];
+    let mut b = ['a', 'a', 'a', 'b', 'b', 'a', 'a'];
+    let mut c = ['a'];
+    let mut d = ['a', 'b', 'b', 'b'];
+    let mut e = ['a', 'b', 'c'];
+
+    let sz = Solution::compress(&mut a);
+    dbg!(sz, a);
+
+    let sz = Solution::compress(&mut b);
+    dbg!(sz, b);
+
+    let sz = Solution::compress(&mut c);
+    dbg!(sz, c);
+
+    let sz = Solution::compress(&mut d);
+    dbg!(sz, d);
+
+    let sz = Solution::compress(&mut e);
+    dbg!(sz, e);
+}
+
+struct Solution;
+
+/*
+ NOTE: the key to making this work was using a separate "start" marker for the start index of the
+       current char; I kept trying to use the "write" variable compared with the read var.
+*/
+
+impl Solution {
+    pub fn compress(chars: &mut [char]) -> i32 {
+        let (mut read, mut write) = (1, 0);
+        let len = chars.len();
+        let mut last = chars[0];
+        let mut start = 0;
+        while read < len {
+            let cur = chars[read];
+            if cur != last {
+                chars[write] = last;
+                last = cur;
+                let count = read - start;
+                start = read;
+                if count > 1 {
+                    for c in Self::tok(count) {
+                        write += 1;
+                        chars[write] = c;
+                    }
+                }
+                write += 1;
+            }
+            read += 1;
+        }
+
+        chars[write] = last;
+        let count = read - start;
+        if count > 1 {
+            for c in Self::tok(count) {
+                write += 1;
+                chars[write] = c;
+            }
+        }
+
+        write as i32 + 1
+    }
+
+    fn tok(num: usize) -> Vec<char> {
+        num.to_string().chars().collect()
+    }
+}