Gym 100513M - Variable Shadowing

In computer programming, variable shadowing occurs when a variable declared within a certain scope has the same nameas a variable declared in an outer scope. The outer variable is said to beshadowed by the inner variable, and this can lead to a confusion. If multipleouter scopes contain variables with the same name, the variable in the nearestscope will be shadowed.

Formally, a declared variable shadows another declared variable if thefollowing conditions are met simultaneously:

·        the othervariable is declared in outer scope and before (in terms of position in programsource code) the declaration of the first variable,

·        the othervariable is nearest among all variables satisfying the condition above.

Here is an example containing exactly one variable shadowing:

/* Prints a+max(b,c) */
int main() {
    int a, b, c;
    cin » a » b » c;
    if (b > c) {
        int a = b; // <– variable 'a'shadows outer 'a'
        int x = c;
        b = x;
        c = a;
    }
    int x = a + c; // <– no shadowinghere
    cout « x « endl;
}

Variable shadowing is permitted in many modern programming languagesincluding C++, but compilers can warn a programmer about variable shadowing toavoid possible mistakes in a code.

Consider a trivial programming language that consists only of scopes andvariable declarations. The program consists of lines, each line contains onlycharacters '{', '}', 'a' ... 'z' separated by one or more spaces.

·        Scopes. A scope (excluding global) is bounded with a pair of matching curlybrackets '{' and '}'. A scope is an inner scope relative to another scope if brackets ofthe first scope are enclosed by brackets of the second scope.

·        Variables. A variable declaration in this language is written just as a name of thevariable. In addition all variables are lowercase Latin letters from 'a' to 'z'inclusive (so there are at most 26 variable names). A variable is declared ineach scope at most once.

Given a syntactically correct program (i.e. curly brackets form a regular bracket sequence), writean analyzer to warn about each fact of variable shadowing. Warnings shouldinclude exact positions of shadowing and shadowed variables. Your output shouldfollow the format shown in the examples below.

Input

The first line contains integer n (1 ≤ n ≤ 50)— the number of lines in theprogram. The following n lines contain the program. Each program line consists of tokens '{', '}', 'a' ... 'z'separated by one or more spaces. The length of each line is between 1 and 50characters. Each program line contains at least one non-space character.

The curly brackets in the program form a regularbracket sequence, so each opening bracket '{' has uniquely defined matching closing bracket '}' and vice versa. A variable is declared in a scope at most once. Anyscope (including global) can be empty, i.e. can contain no variabledeclarations.

Output

For each fact of shadowing write a line in form "r1:c1:warning: shadowed declaration of ?, the shadowed position is r2:c2", where "r1:c1" is the number of line and position in line of shadowingdeclaration and "r2:c2" is the number of line and position in line of shadoweddeclaration. Replace '?' with the letter 'a' ... 'z' — the nameof shadowing/shadowed variable. If multiple outer scopes have variables namedas the shadowing variable, the variable in the nearest outer scope is shadowed.

Print warnings in increasing order of r1, or in increasing order of c1 if values r1 are equal. Leave the output empty if there are no variable shadowings.

Sample test(s)

input

1
{ a { b { a } } } b

output

1:11:warning: shadowed declaration of a, the shadowed position is 1:3

input

1
{ a { a { a } } }

output

1:7: warning:shadowed declaration of a, the shadowed position is 1:3
1:11: warning: shadowed declaration of a, the shadowed position is 1:7

input

7
a b {
 a { a }
 c   b {
  c
 } }
{ a d z
} z

output

2:2: warning:shadowed declaration of a, the shadowed position is 1:1
2:6: warning: shadowed declaration of a, the shadowed position is 2:2
3:6: warning: shadowed declaration of b, the shadowed position is 1:3
4:3: warning: shadowed declaration of c, the shadowed position is 3:2
6:3: warning: shadowed declaration of a, the shadowed position is 1:1

input

1
{ a } { b } a { a } { a } { a x { a b x } } b x

output

1:17:warning: shadowed declaration of a, the shadowed position is 1:13
1:23: warning: shadowed declaration of a, the shadowed position is 1:13
1:29: warning: shadowed declaration of a, the shadowed position is 1:13
1:35: warning: shadowed declaration of a, the shadowed position is 1:29
1:39: warning: shadowed declaration of x, the shadowed position is 1:31

 

思路：

模拟，用栈来判断如今在第几层括号，另外开数组记录当前有哪些变量及个数，注意以下细节就能过

程序：#define _CRT_SECURE_NO_WARNINGS#include <iostream>#include <cstring>#include <cstdio>#include <stack>using namespace std;const int N = 100005;struct node{int x, y;};int step[N];char var[N];int main(){stack<node> q[200];memset(step, 0, sizeof(step));node temp;int n;scanf("%d\n", &n);int i, num = 0, v = 0;char st[N];for (i = 1; i <= n; i++){cin.getline(st, N, '\n');int len = strlen(st);int j;for (j = 0; j<len; j++){if (st[j] == ' ')continue;if (st[j] == '{'){num++;}elseif (st[j] == '}'){for (; step[num]>0; step[num]--){q[var[v - 1]].pop();v--;}num--;//                    cout<<step[num]<<endl;}else{if (!q[st[j]].empty()){printf("%d:%d: warning: shadowed declaration of %c, the shadowed position is %d:%d\n", i, j + 1, st[j], q[st[j]].top().x, q[st[j]].top().y);}temp.x = i;temp.y = j + 1;q[st[j]].push(temp);var[v++] = st[j];step[num]++;}}}return 0;}