1、纯for循环

for (int i = 0; i < arr.length; i++) {            for (int j = i + 1; j < arr.length; j++) {                if (arr[i] + arr[j] == 100) {                    System.out.println(arr[i] + ":" + arr[j]);                }            }        }

2、卡住一个端，左端只有小于M/2才会判断 

for (int i = 0; i < arr.length; i++) {            if (arr[i] <= 100 / 2) {                for (int j = i + 1; j < arr.length; j++) {                    if (arr[i] + arr[j] == 100) {                        System.out.println(arr[i] + ":" + arr[j]);                    }                }            }        }

3、卡住一个端，左端只有小于M/2，右端大于M/2才会判断 

for (int i = 0; i < arr.length; i++) {            if (arr[i] <= 100 / 2) {                for (int j = i + 1; j < arr.length; j++) {                    if (arr[j] >= 100 / 2) {                        if (arr[i] + arr[j] == 100) {                            System.out.println(arr[i] + ":" + arr[j]);                        }                    }                }            }        }