LeetCode OJ 150. Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Some examples:

  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
  ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

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解答：

这道题只要注意有负数就可以了。

int evalRPN(char** tokens, int tokensSize) {
    int stack[tokensSize];
    , sum, i, j;

    ; i < tokensSize; i++){
        '){
            sum = ;
            ; tokens[i][j] != ; j++){
                sum = sum *  + tokens[i][j] - ';
            }
            stack[++top] = sum;
        }
        else{
            if('+' == *(tokens[i])){
                stack[top - ] = stack[top - ] + stack[top];
            }
            else if('-' == *(tokens[i])){
                 == tokens[i][])
                    stack[top - ] = stack[top - ] - stack[top];
                else{
                    sum = ;
                    ; tokens[i][j] != ; j++){
                        sum = sum *  + tokens[i][j] - ';
                    }
                    stack[++top] = -sum;
                    continue;
                }
            }
            else if('*' == *(tokens[i])){
                stack[top - ] = stack[top - ] * stack[top];
            }
            else if('/' == *(tokens[i])){
                stack[top - ] = stack[top - ] / stack[top];
            }
            top--;
        }
    }
    return stack[top];
}