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Initialization
M[i][j] = 1 means person i knows person j. Tally knowMe[j] (how many know j) and Iknow[i] (how many i knows) across the whole matrix, then look for the person with knowMe = n−1 and Iknow = 0.
Brute Force
1function celebrity(M) {2 const n = M.length;3 const knowMe = new Array(n).fill(0);4 const Iknow = new Array(n).fill(0);//n: 45 for (let i = 0; i < n; i++) {6 for (let j = 0; j < n; j++) {7 if (M[i][j] == 1) {8 knowMe[j]++;9 Iknow[i]++;10 }11 }12 }13 for (let i = 0; i < n; i++) {14 if (knowMe[i] == n - 1 && Iknow[i] == 0) {15 return i;16 }17 }18 return -1;19}