1545. 找出第 N 个二进制字符串中的第 K 位

src/main.rs

@@ -1,50 +1,48 @@
+use std::cell::RefCell;
+
 struct Solution;
 mod arr;
-
 impl Solution {
-    pub fn min_swaps(grid: Vec<Vec<i32>>) -> i32 {
-        fn count_tail_zero(arr: &Vec<i32>) -> i32 {
-            let mut cnt = 0;
-            for i in (0..arr.len()).rev() {
-                if arr[i] == 0 {
-                    cnt += 1;
-                } else {
-                    return cnt;
-                }
-            }
-            cnt
+    pub fn find_kth_bit(n: i32,mut k: i32) -> char {
+        let len = Self::get_length_arr()(n);
+        if n == 1 || k == 0 {
+            return '0';
         }
-        let mut arr = Vec::<i32>::with_capacity(grid.len());
-        for i in 0..grid[0].len() {
-            arr.push(count_tail_zero(&grid[i]))
+        if k == len / 2 + 1 {
+            return '1';
         }
-        let mut cnt = 0;
-        for i in (0..grid.len()).rev() {
-            let mut index = 0;
-            let mut cant = true;
-            for j in 0..arr.len() {
-                if arr[j] == -1 {
-                    continue;
-                }
-                if arr[j] >= i as i32 {
-                    arr[j] = -1;
-                    cnt += index;
-                    cant = false;
-                    break;
-                }
-                index += 1;
+        if k > len / 2 + 1 {
+            if Self::find_kth_bit(n - 1, (len / 2+1) - (k - (len / 2 + 1))) == '1' {
+                '0'
+            } else {
+                '1'
             }
-            if cant{
-                return -1;
+        } else {
+            Self::find_kth_bit(n - 1, k)
+        }
+    }
+    fn get_length_arr() -> impl Fn(i32) -> i32 {
+        let cell = RefCell::new(None);
+        move |n| {
+            let mut value = cell.borrow_mut();
+            if value.is_none() {
+                let mut arr = Vec::with_capacity(20);
+                arr.push(1);
+                for _ in 1..20 {
+                    arr.push(arr[arr.len() - 1] * 2 + 1);
+                }
+                *value = Some(arr);
+            }
+            if let Some(x) = value.as_ref() {
+                x[n as usize - 1]
+            } else {
+                0
             }
         }
-        cnt
     }
 }
 
 fn main() {
-    let result = Solution::min_swaps(arr::make_matrix(
-        "[[0,0,1],[1,1,0],[1,0,0]]",
-    ));
+    let result = Solution::find_kth_bit(4, 14);
     println!("{:?}", result);
 }