add snail sort in odin.

snail.odin

@@ -0,0 +1,51 @@
+package main
+import "core:fmt"
+
+snail :: proc(xss: [][]int) -> [dynamic]int {
+    yss := [dynamic]int{}
+
+    h := len(xss)
+    if h == 0 { return yss }
+    w := len(xss[0])
+    if w == 0 { return yss }
+
+    for b in 0..=max(h, w) {
+        ex := w - b - 1
+        ey := h - b - 1
+
+        for c in b..=ex            { append(&yss, xss[b][c]) }
+        for r in (b + 1)..=ey      { append(&yss, xss[r][ex]) }
+
+        if ex == b || ey == b { return yss }
+
+        for c_off in b..<ex        { append(&yss, xss[ey][ex - 1 - c_off]) }
+        for r_off in (b + 1)..<ey  { append(&yss, xss[ey - r_off][b]) }
+    }
+
+    return yss
+}
+
+eq :: proc(a: []$T, b: []$S) -> bool {
+    if len(a) != len(b) { return false }
+    for i in 0..<len(a) {
+        if a[i] != b[i] { return false }
+    }
+    return true
+}
+
+
+main :: proc() {
+    initial := [][]int{ {1, 2, 3}, {4, 5, 6}, {7, 8, 9} }
+    expected := [dynamic]int{1, 2, 3, 6, 9, 8, 7, 4, 5}
+    fmt.println(eq(snail(initial)[:], expected[:]))
+
+    initial = [][]int{ {1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12} }
+    expected = {1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7}
+    fmt.println(eq(snail(initial)[:], expected[:]))
+
+    initial = [][]int{ {1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, 12}, {13, 14, 15} }
+    expected = [dynamic]int{1, 2, 3, 6, 9, 12, 15, 14, 13, 10, 7, 4, 5, 8, 11}
+    fmt.println(eq(snail(initial)[:], expected[:]))
+
+    fmt.println("all tests passed.")
+}