行星碰撞（ 暴力从左遍历 + 栈）

i >= 0这个条件，属于边界条件，不写会卡用例，1， -2， -2， -2。

import java.util.Arrays;

class Suit {
    public static int[] asteroidCollision(int[] asteroids) {
        int len = asteroids.length;
        int size = len;
        for (int i = 0; i < size - 1; i++) {  // 屏蔽住 i--, 可以看到编译器显示的问题，并没有累加
            if (i >= 0 && asteroids[i] > 0 && asteroids[i + 1] < 0) {// i >=0 卡测试用例1， -2， -2， -2
                if (Math.abs(asteroids[i]) > Math.abs(asteroids[i + 1])) {
                    for (int j = i + 2; j < len; j++) {
                        asteroids[j - 1] = asteroids[j];
                    }
                    i--;
                    size--;
                } else if (Math.abs(asteroids[i]) == Math.abs(asteroids[i + 1])) {
                    for (int j = i + 2; j < len; j++) {
                        asteroids[j - 2] = asteroids[j];
                    }
                    size -= 2;
                    i -= 2;
                } else {
                    for (int j = i + 1; j < len; j++) {
                        asteroids[j - 1] = asteroids[j];
                    }
                    i -= 2;
                    size--;
                }
                if (size == 0) {
                    return new int[] {};
                }
            }

        }
        int[] result = new int[size];
        System.arraycopy(asteroids, 0, result, 0, size);
        return result;

    }

    public static void main(String[] args) {
        System.out.println(Arrays.toString(asteroidCollision(new int[]{1,-2,-2,-2})));
    }
}

import java.util.Arrays;
import java.util.Stack;

class Asteroids {
    public static int[] asteroidCollision(int[] asteroids) {
        Stack stack = new Stack<>();
        int len = asteroids.length;//还是抽出来吧
        for (int i = 0; i < len; i++){
            if(asteroids[i] > 0){
                stack.push(asteroids[i]);
            }else if(asteroids[i] < 0){
                if(stack.isEmpty() || stack.peek() < 0){ // peek前要判空的
                    stack.push(asteroids[i]);
                    continue;
                }
                boolean isEquals = false;//相等的情况，边界条件
                if(Math.abs(asteroids[i]) > Math.abs(stack.peek())){
                    while(!stack.isEmpty() && stack.peek() > 0){
                        int ele = stack.peek();
                        if(Math.abs(ele) < Math.abs(asteroids[i])){
                            stack.pop();
                        }else if(Math.abs(ele) == Math.abs(asteroids[i])) { //相等的情况一定要考虑到
                            stack.pop();
                            isEquals = true;
                            break;
                        }else{
                            break;
                        }
                    }
                    if(isEquals == true){
                        isEquals = false;
                        continue;
                    }
                    if( stack.isEmpty() || stack.peek() < 0){ //注意条件的先后顺序
                        stack.push(asteroids[i]);
                    }
                }else if(Math.abs(asteroids[i]) < Math.abs(stack.peek())){
                    continue;
                }else {
                    stack.pop();
                }
            }else {
                System.out.println("测试用例含有0");
            }
        }
        int[] ans = new int[stack.size()];
        for (int t = ans.length - 1; t >= 0; --t) {
            ans[t] = stack.pop();
        }
        return ans;
    }

    public static void main(String[] args) {
        //1,-2,-2,-2
        //-2,-1,1,2
        System.out.println(Arrays.toString(asteroidCollision(new int[]{-2,2,1,-2})));
    }
}