feat(geektime_algo): add 39 back tracking bag_exec

Author: caitlingao

rust/39_back_tracking/bag_exec.rs

@@ -0,0 +1,76 @@
+use std::collections::HashMap;
+
+fn solve_bag(items: Vec<(i32, i32)>, capacity: i32) -> HashMap<i32, Vec<i32>> {
+    let pick_idx       = 0;
+    let current_weight = 0;
+    let mut picks      = vec![-1; items.len()];
+    let mut max_values = vec![-1; items.len()];
+    let mut result     = HashMap::new();
+
+    bag(pick_idx,
+        current_weight,
+        &items,
+        capacity,
+        &mut picks,
+        &mut max_values,
+        &mut result,);
+
+    result
+}
+
+fn bag(pick_idx:       i32,
+       current_weight: i32,
+       items:          &Vec<(i32, i32)>,
+       capacity:       i32,
+       picks:          &mut Vec<i32>,
+       max_values:     &mut Vec<i32>,
+       result:         &mut HashMap<i32, Vec<i32>>) {
+   if current_weight == capacity || pick_idx == items.len() as i32 {
+       if get_value(items, &picks) > get_value(items, max_values) {
+           for i in 0..picks.len() {
+            max_values[i] = picks[i];
+           }
+           result.insert(get_value(items, max_values), picks.to_vec());
+       }
+       return;
+   }
+
+   // 选
+   let item_weight = items[pick_idx as usize].0;
+   if current_weight + item_weight <= capacity {
+       picks[pick_idx as usize] = 1;
+       bag(pick_idx + 1,
+           current_weight + item_weight,
+           items,
+           capacity,
+           picks,
+           max_values,
+           result);
+   }
+
+   // 不选
+   picks[pick_idx as usize] = 0;
+   bag(pick_idx + 1,
+       current_weight,
+       items,
+       capacity,
+       picks,
+       max_values,
+       result);
+
+}
+
+fn get_value(items: &Vec<(i32, i32)>, picks: &Vec<i32>) -> i32 {
+    let mut result = 0;
+    for i in 0..picks.len() {
+        if picks[i] == 1 { result += items[i].1; }
+    }
+    result
+}
+
+fn main() {
+    // [(weight, value)...]
+    let items = vec![(3, 5), (2, 2), (1, 4), (1, 2), (4, 10)];
+    let m = solve_bag(items, 10);
+    println!("{:?}", m); // {13: [1, 1, 1, 1, 0], 21: [1, 1, 1, 0, 1]}
+}