zig : upgrade codes && rust : add codes for chapter_searching and chapter_dynamic_programming. (#591)

* zig : update zig codes

* rust : add codes for linear_search and hashing_search

* rust : add codes for linear_search and hashing_search

* rust : add codes for chapter_dynamic_programming

codes/zig/chapter_searching/two_sum.zig

@@ -14,7 +14,7 @@ pub fn twoSumBruteForce(nums: []i32, target: i32) ?[2]i32 {
         var j = i + 1;
         while (j < size) : (j += 1) {
             if (nums[i] + nums[j] == target) {
-                return [_]i32{@intCast(i32, i), @intCast(i32, j)};
+                return [_]i32{@intCast(i), @intCast(j)};
             }
         }
     }
@@ -31,9 +31,9 @@ pub fn twoSumHashTable(nums: []i32, target: i32) !?[2]i32 {
     // 单层循环，时间复杂度 O(n)
     while (i < size) : (i += 1) {
         if (dic.contains(target - nums[i])) {
-            return [_]i32{dic.get(target - nums[i]).?, @intCast(i32, i)};
+            return [_]i32{dic.get(target - nums[i]).?, @intCast(i)};
         }
-        try dic.put(nums[i], @intCast(i32, i));
+        try dic.put(nums[i], @intCast(i));
     }
     return null;
 }